Finally, here's something experimental. It increases native aggressiveness in North America until a wave of plauges reduce it to the normal values in the late 1500s. Note that there are a couple of aggressiveness-raising events; native aggressiveness isn't stored in the savegame, so I had to resort to this

.
These might keep colonies from being founded too early .
#Natives up
event ={
id = 17024
random = no
name = "The North American Natives"
desc = "The natives of North America were numerous and well-organized. Until European diseases decimated them, any attempt at colonization would require a major military expedition"
date = { day = 15 month = january year = 1492 }
style = 1
action_a ={
name = "Let's look at the Carribean instead, then"
command = { type = natives which = 115 value = 9 }
command = { type = natives which = 112 value = 9 }
command = { type = natives which = 114 value = 9 }
command = { type = natives which = 117 value = 9 }
command = { type = natives which = 113 value = 9 }
command = { type = natives which = 116 value = 9 }
command = { type = natives which = 100 value = 9 }
command = { type = natives which = 61 value = 9 }
command = { type = natives which = 66 value = 9 }
command = { type = natives which = 62 value = 9 }
command = { type = natives which = 65 value = 9 }
command = { type = natives which = 88 value = 9 }
command = { type = natives which = 68 value = 9 }
command = { type = natives which = 86 value = 9 }
command = { type = natives which = 87 value = 9 }
command = { type = natives which = 69 value = 9 }
command = { type = natives which = 64 value = 9 }
command = { type = natives which = 63 value = 9 }
command = { type = natives which = 70 value = 9 }
command = { type = natives which = 85 value = 9 }
command = { type = natives which = 99 value = 9 }
command = { type = natives which = 84 value = 9 }
command = { type = natives which = 50 value = 9 }
command = { type = natives which = 49 value = 9 }
command = { type = natives which = 48 value = 9 }
command = { type = natives which = 55 value = 9 }
command = { type = natives which = 54 value = 9 }
command = { type = natives which = 56 value = 9 }
command = { type = natives which = 82 value = 9 }
command = { type = natives which = 72 value = 9 }
command = { type = natives which = 98 value = 9 }
command = { type = natives which = 81 value = 9 }
command = { type = natives which = 92 value = 9 }
command = { type = natives which = 95 value = 9 }
command = { type = natives which = 96 value = 9 }
command = { type = natives which = 97 value = 9 }
command = { type = natives which = 93 value = 9 }
command = { type = natives which = 131 value = 9 }
command = { type = natives which = 134 value = 9 }
command = { type = natives which = 130 value = 9 }
command = { type = natives which = 135 value = 9 }
command = { type = natives which = 129 value = 9 }
command = { type = natives which = 136 value = 9 }
command = { type = natives which = 128 value = 9 }
command = { type = natives which = 132 value = 9 }
command = { type = natives which = 78 value = 9 }
command = { type = natives which = 73 value = 9 }
command = { type = natives which = 59 value = 9 }
command = { type = natives which = 60 value = 9 }
command = { type = natives which = 74 value = 9 }
command = { type = natives which = 80 value = 9 }
command = { type = natives which = 75 value = 9 }
command = { type = natives which = 76 value = 9 }
command = { type = natives which = 58 value = 9 }
command = { type = natives which = 123 value = 9 }
command = { type = natives which = 124 value = 9 }
command = { type = natives which = 125 value = 9 }
command = { type = natives which = 126 value = 9 }
command = { type = natives which = 127 value = 9 }
command = { type = natives which = 51 value = 9 }
command = { type = natives which = 45 value = 9 }
command = { type = natives which = 46 value = 9 }
command = { type = natives which = 57 value = 9 }
command = { type = natives which = 47 value = 9 }
command = { type = natives which = 53 value = 9 }
command = { type = natives which = 52 value = 9 }
command = { type = natives which = 102 value = 9 }
command = { type = natives which = 103 value = 9 }
command = { type = natives which = 105 value = 9 }
command = { type = natives which = 104 value = 9 }
command = { type = natives which = 101 value = 9 }
command = { type = natives which = 118 value = 9 }
command = { type = natives which = 119 value = 9 }
command = { type = natives which = 120 value = 9 }
command = { type = natives which = 71 value = 9 }
command = { type = natives which = 83 value = 9 }
command = { type = natives which = 67 value = 9 }
command = { type = natives which = 90 value = 9 }
command = { type = natives which = 91 value = 9 }
command = { type = natives which = 89 value = 9 }
command = { type = natives which = 111 value = 9 }
command = { type = natives which = 106 value = 9 }
command = { type = natives which = 108 value = 9 }
command = { type = natives which = 122 value = 9 }
command = { type = natives which = 107 value = 9 }
command = { type = natives which = 121 value = 9 }
command = { type = natives which = 109 value = 9 }
command = { type = natives which = 110 value = 9 }
command = { type = natives which = 42 value = 9 }
command = { type = natives which = 1480 value = 9 }
command = { type = natives which = 43 value = 9 }
command = { type = natives which = 40 value = 9 }
command = { type = natives which = 41 value = 9 }
command = { type = natives which = 44 value = 9 }
}
}
#Natives up
event ={
id = 17025
random = no
name = "The North American Natives"
desc = "The natives of North America were numerous and well-organized. Until European diseases decimated them, any attempt at colonization would require a major military expedition"
date = { day = 15 month = january year = 1522 }
style = 1
action_a ={
name = "Let's look at the Carribean instead, then"
command = { type = natives which = 115 value = 9 }
command = { type = natives which = 112 value = 9 }
command = { type = natives which = 114 value = 9 }
command = { type = natives which = 117 value = 9 }
command = { type = natives which = 113 value = 9 }
command = { type = natives which = 116 value = 9 }
command = { type = natives which = 100 value = 9 }
command = { type = natives which = 61 value = 9 }
command = { type = natives which = 66 value = 9 }
command = { type = natives which = 62 value = 9 }
command = { type = natives which = 65 value = 9 }
command = { type = natives which = 88 value = 9 }
command = { type = natives which = 68 value = 9 }
command = { type = natives which = 86 value = 9 }
command = { type = natives which = 87 value = 9 }
command = { type = natives which = 69 value = 9 }
command = { type = natives which = 64 value = 9 }
command = { type = natives which = 63 value = 9 }
command = { type = natives which = 70 value = 9 }
command = { type = natives which = 85 value = 9 }
command = { type = natives which = 99 value = 9 }
command = { type = natives which = 84 value = 9 }
command = { type = natives which = 50 value = 9 }
command = { type = natives which = 49 value = 9 }
command = { type = natives which = 48 value = 9 }
command = { type = natives which = 55 value = 9 }
command = { type = natives which = 54 value = 9 }
command = { type = natives which = 56 value = 9 }
command = { type = natives which = 82 value = 9 }
command = { type = natives which = 72 value = 9 }
command = { type = natives which = 98 value = 9 }
command = { type = natives which = 81 value = 9 }
command = { type = natives which = 92 value = 9 }
command = { type = natives which = 95 value = 9 }
command = { type = natives which = 96 value = 9 }
command = { type = natives which = 97 value = 9 }
command = { type = natives which = 93 value = 9 }
command = { type = natives which = 131 value = 9 }
command = { type = natives which = 134 value = 9 }
command = { type = natives which = 130 value = 9 }
command = { type = natives which = 135 value = 9 }
command = { type = natives which = 129 value = 9 }
command = { type = natives which = 136 value = 9 }
command = { type = natives which = 128 value = 9 }
command = { type = natives which = 132 value = 9 }
command = { type = natives which = 78 value = 9 }
command = { type = natives which = 73 value = 9 }
command = { type = natives which = 59 value = 9 }
command = { type = natives which = 60 value = 9 }
command = { type = natives which = 74 value = 9 }
command = { type = natives which = 80 value = 9 }
command = { type = natives which = 75 value = 9 }
command = { type = natives which = 76 value = 9 }
command = { type = natives which = 58 value = 9 }
command = { type = natives which = 123 value = 9 }
command = { type = natives which = 124 value = 9 }
command = { type = natives which = 125 value = 9 }
command = { type = natives which = 126 value = 9 }
command = { type = natives which = 127 value = 9 }
command = { type = natives which = 51 value = 9 }
command = { type = natives which = 45 value = 9 }
command = { type = natives which = 46 value = 9 }
command = { type = natives which = 57 value = 9 }
command = { type = natives which = 47 value = 9 }
command = { type = natives which = 53 value = 9 }
command = { type = natives which = 52 value = 9 }
command = { type = natives which = 102 value = 9 }
command = { type = natives which = 103 value = 9 }
command = { type = natives which = 105 value = 9 }
command = { type = natives which = 104 value = 9 }
command = { type = natives which = 101 value = 9 }
command = { type = natives which = 118 value = 9 }
command = { type = natives which = 119 value = 9 }
command = { type = natives which = 120 value = 9 }
command = { type = natives which = 71 value = 9 }
command = { type = natives which = 83 value = 9 }
command = { type = natives which = 67 value = 9 }
command = { type = natives which = 90 value = 9 }
command = { type = natives which = 91 value = 9 }
command = { type = natives which = 89 value = 9 }
command = { type = natives which = 111 value = 9 }
command = { type = natives which = 106 value = 9 }
command = { type = natives which = 108 value = 9 }
command = { type = natives which = 122 value = 9 }
command = { type = natives which = 107 value = 9 }
command = { type = natives which = 121 value = 9 }
command = { type = natives which = 109 value = 9 }
command = { type = natives which = 110 value = 9 }
command = { type = natives which = 42 value = 9 }
command = { type = natives which = 1480 value = 9 }
command = { type = natives which = 43 value = 9 }
command = { type = natives which = 40 value = 9 }
command = { type = natives which = 41 value = 9 }
command = { type = natives which = 44 value = 9 }
}
}#Natives up
event ={
id = 17026
random = no
name = "The North American Natives"
desc = "The natives of North America were numerous and well-organized. Until European diseases decimated them, any attempt at colonization would require a major military expedition"
date = { day = 15 month = january year = 1552 }
style = 1
action_a ={
name = "Let's look at the Carribean instead, then"
command = { type = natives which = 115 value = 9 }
command = { type = natives which = 112 value = 9 }
command = { type = natives which = 114 value = 9 }
command = { type = natives which = 117 value = 9 }
command = { type = natives which = 113 value = 9 }
command = { type = natives which = 116 value = 9 }
command = { type = natives which = 100 value = 9 }
command = { type = natives which = 61 value = 9 }
command = { type = natives which = 66 value = 9 }
command = { type = natives which = 62 value = 9 }
command = { type = natives which = 65 value = 9 }
command = { type = natives which = 88 value = 9 }
command = { type = natives which = 68 value = 9 }
command = { type = natives which = 86 value = 9 }
command = { type = natives which = 87 value = 9 }
command = { type = natives which = 69 value = 9 }
command = { type = natives which = 64 value = 9 }
command = { type = natives which = 63 value = 9 }
command = { type = natives which = 70 value = 9 }
command = { type = natives which = 85 value = 9 }
command = { type = natives which = 99 value = 9 }
command = { type = natives which = 84 value = 9 }
command = { type = natives which = 50 value = 9 }
command = { type = natives which = 49 value = 9 }
command = { type = natives which = 48 value = 9 }
command = { type = natives which = 55 value = 9 }
command = { type = natives which = 54 value = 9 }
command = { type = natives which = 56 value = 9 }
command = { type = natives which = 82 value = 9 }
command = { type = natives which = 72 value = 9 }
command = { type = natives which = 98 value = 9 }
command = { type = natives which = 81 value = 9 }
command = { type = natives which = 92 value = 9 }
command = { type = natives which = 95 value = 9 }
command = { type = natives which = 96 value = 9 }
command = { type = natives which = 97 value = 9 }
command = { type = natives which = 93 value = 9 }
command = { type = natives which = 131 value = 9 }
command = { type = natives which = 134 value = 9 }
command = { type = natives which = 130 value = 9 }
command = { type = natives which = 135 value = 9 }
command = { type = natives which = 129 value = 9 }
command = { type = natives which = 136 value = 9 }
command = { type = natives which = 128 value = 9 }
command = { type = natives which = 132 value = 9 }
command = { type = natives which = 78 value = 9 }
command = { type = natives which = 73 value = 9 }
command = { type = natives which = 59 value = 9 }
command = { type = natives which = 60 value = 9 }
command = { type = natives which = 74 value = 9 }
command = { type = natives which = 80 value = 9 }
command = { type = natives which = 75 value = 9 }
command = { type = natives which = 76 value = 9 }
command = { type = natives which = 58 value = 9 }
command = { type = natives which = 123 value = 9 }
command = { type = natives which = 124 value = 9 }
command = { type = natives which = 125 value = 9 }
command = { type = natives which = 126 value = 9 }
command = { type = natives which = 127 value = 9 }
command = { type = natives which = 51 value = 9 }
command = { type = natives which = 45 value = 9 }
command = { type = natives which = 46 value = 9 }
command = { type = natives which = 57 value = 9 }
command = { type = natives which = 47 value = 9 }
command = { type = natives which = 53 value = 9 }
command = { type = natives which = 52 value = 9 }
command = { type = natives which = 102 value = 9 }
command = { type = natives which = 103 value = 9 }
command = { type = natives which = 105 value = 9 }
command = { type = natives which = 104 value = 9 }
command = { type = natives which = 101 value = 9 }
command = { type = natives which = 118 value = 9 }
command = { type = natives which = 119 value = 9 }
command = { type = natives which = 120 value = 9 }
command = { type = natives which = 71 value = 9 }
command = { type = natives which = 83 value = 9 }
command = { type = natives which = 67 value = 9 }
command = { type = natives which = 90 value = 9 }
command = { type = natives which = 91 value = 9 }
command = { type = natives which = 89 value = 9 }
command = { type = natives which = 111 value = 9 }
command = { type = natives which = 106 value = 9 }
command = { type = natives which = 108 value = 9 }
command = { type = natives which = 122 value = 9 }
command = { type = natives which = 107 value = 9 }
command = { type = natives which = 121 value = 9 }
command = { type = natives which = 109 value = 9 }
command = { type = natives which = 110 value = 9 }
command = { type = natives which = 42 value = 9 }
command = { type = natives which = 1480 value = 9 }
command = { type = natives which = 43 value = 9 }
command = { type = natives which = 40 value = 9 }
command = { type = natives which = 41 value = 9 }
command = { type = natives which = 44 value = 9 }
}
}
#Natives down
event ={
id = 17027
random = no
name = "Plague in the Americas"
desc = "As wave after wave of plagues overcame their communities, the native peoples became demoralized, and were easily displaced by European colonists"
date = { day = 11 month = january year = 1595 }
offset = 6000
style = 3
action_a ={
name = "OK"
command = { type = natives which = 115 value = 3 }
command = { type = natives which = 112 value = 8 }
command = { type = natives which = 114 value = 3 }
command = { type = natives which = 117 value = 1 }
command = { type = natives which = 113 value = 9 }
command = { type = natives which = 116 value = 1 }
command = { type = natives which = 100 value = 8 }
command = { type = natives which = 61 value = 9 }
command = { type = natives which = 66 value = 7 }
command = { type = natives which = 62 value = 7 }
command = { type = natives which = 65 value = 2 }
command = { type = natives which = 88 value = 5 }
command = { type = natives which = 68 value = 2 }
command = { type = natives which = 86 value = 3 }
command = { type = natives which = 87 value = 1 }
command = { type = natives which = 69 value = 2 }
command = { type = natives which = 64 value = 2 }
command = { type = natives which = 63 value = 5 }
command = { type = natives which = 70 value = 6 }
command = { type = natives which = 85 value = 8 }
command = { type = natives which = 99 value = 9 }
command = { type = natives which = 84 value = 9 }
command = { type = natives which = 50 value = 9 }
command = { type = natives which = 49 value = 9 }
command = { type = natives which = 48 value = 9 }
command = { type = natives which = 55 value = 7 }
command = { type = natives which = 54 value = 3 }
command = { type = natives which = 56 value = 8 }
command = { type = natives which = 82 value = 7 }
command = { type = natives which = 72 value = 6 }
command = { type = natives which = 98 value = 9 }
command = { type = natives which = 81 value = 5 }
command = { type = natives which = 92 value = 8 }
command = { type = natives which = 95 value = 7 }
command = { type = natives which = 96 value = 6 }
command = { type = natives which = 97 value = 8 }
command = { type = natives which = 93 value = 6 }
command = { type = natives which = 131 value = 5 }
command = { type = natives which = 134 value = 6 }
command = { type = natives which = 130 value = 5 }
command = { type = natives which = 135 value = 1 }
command = { type = natives which = 129 value = 1 }
command = { type = natives which = 136 value = 2 }
command = { type = natives which = 128 value = 1 }
command = { type = natives which = 132 value = 6 }
command = { type = natives which = 78 value = 6 }
command = { type = natives which = 73 value = 7 }
command = { type = natives which = 59 value = 7 }
command = { type = natives which = 60 value = 6 }
command = { type = natives which = 74 value = 8 }
command = { type = natives which = 80 value = 6 }
command = { type = natives which = 75 value = 7 }
command = { type = natives which = 76 value = 6 }
command = { type = natives which = 58 value = 7 }
command = { type = natives which = 123 value = 1 }
command = { type = natives which = 124 value = 1 }
command = { type = natives which = 125 value = 2 }
command = { type = natives which = 126 value = 1 }
command = { type = natives which = 127 value = 1 }
command = { type = natives which = 51 value = 7 }
command = { type = natives which = 45 value = 3 }
command = { type = natives which = 46 value = 3 }
command = { type = natives which = 57 value = 6 }
command = { type = natives which = 47 value = 8 }
command = { type = natives which = 53 value = 5 }
command = { type = natives which = 52 value = 8 }
command = { type = natives which = 102 value = 9 }
command = { type = natives which = 103 value = 4 }
command = { type = natives which = 105 value = 7 }
command = { type = natives which = 104 value = 7 }
command = { type = natives which = 101 value = 6 }
command = { type = natives which = 118 value = 0 }
command = { type = natives which = 119 value = 0 }
command = { type = natives which = 120 value = 0 }
command = { type = natives which = 71 value = 8 }
command = { type = natives which = 83 value = 9 }
command = { type = natives which = 67 value = 8 }
command = { type = natives which = 90 value = 9 }
command = { type = natives which = 91 value = 9 }
command = { type = natives which = 89 value = 9 }
command = { type = natives which = 111 value = 2 }
command = { type = natives which = 106 value = 3 }
command = { type = natives which = 108 value = 5 }
command = { type = natives which = 122 value = 2 }
command = { type = natives which = 107 value = 6 }
command = { type = natives which = 121 value = 3 }
command = { type = natives which = 109 value = 6 }
command = { type = natives which = 110 value = 1 }
command = { type = natives which = 42 value = 7 }
command = { type = natives which = 1480 value = 3 }
command = { type = natives which = 43 value = 6 }
command = { type = natives which = 40 value = 5 }
command = { type = natives which = 41 value = 5 }
command = { type = natives which = 44 value = 5 }
}
}