How to become king in no time and cost-free:
1) Start as Bohemia
2) Join independence faction and wait about a year when the faction either starts massive rebellion which it easily wins or you get independence via ultimatum.
3) Join Poland
4) Pause once you join. Start faction to install your wife to the throne, send ultimatum right away and ask half the Poland to join your war against the king that follows -> easy victory.
Now you just need to change to elective in Bohemia and choose your second son as your heir (who is heir of your wife) and wait to die.
But you can do more!
5) Get independence on your wife.
6 or 7) Kill David, the heir to Hungary.
7 or 6) Join Hungary.
8) Start faction to install your first son to the throne and send ultimatum right away. Ask half Hungary to join you for easy victory.
9) Kill your son becoming king of Hungary.
Now wait again to die so your son inherits both Poland and Hungary and can form Bohemia unless you manage it in your lifetime.
Long story short, previously it took at least decades to form central European empire. Now it takes literally just few years!
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Here's what's wrong:
In EU3 AI takes into consideration your power and you won't be able to join HRE if you are too powerful which is very close mechanic to swearing fealty in CK2. In CK2 however AI just sees your land as wonderful addition the more powerful you are. But since Bohemia is huge double-duchy+1province at the start you immidiately become major power inside both Poland and Hungary easily getting over 100 % faction power alone. And since in all kingdoms half of it hates the ruler you can ask many people to join your war even though they are not part of your faction.
What should be fixed:
1) Swearing fealty should be available only to your de iure liege as is the case for kingdoms.
2) Being able to ask other vassals to join your faction war even though they were not part of your faction seems a bit OP to me.
1) Start as Bohemia
2) Join independence faction and wait about a year when the faction either starts massive rebellion which it easily wins or you get independence via ultimatum.
3) Join Poland
4) Pause once you join. Start faction to install your wife to the throne, send ultimatum right away and ask half the Poland to join your war against the king that follows -> easy victory.
Now you just need to change to elective in Bohemia and choose your second son as your heir (who is heir of your wife) and wait to die.
But you can do more!
5) Get independence on your wife.
6 or 7) Kill David, the heir to Hungary.
7 or 6) Join Hungary.
8) Start faction to install your first son to the throne and send ultimatum right away. Ask half Hungary to join you for easy victory.
9) Kill your son becoming king of Hungary.
Now wait again to die so your son inherits both Poland and Hungary and can form Bohemia unless you manage it in your lifetime.
Long story short, previously it took at least decades to form central European empire. Now it takes literally just few years!
-----------------------
Here's what's wrong:
In EU3 AI takes into consideration your power and you won't be able to join HRE if you are too powerful which is very close mechanic to swearing fealty in CK2. In CK2 however AI just sees your land as wonderful addition the more powerful you are. But since Bohemia is huge double-duchy+1province at the start you immidiately become major power inside both Poland and Hungary easily getting over 100 % faction power alone. And since in all kingdoms half of it hates the ruler you can ask many people to join your war even though they are not part of your faction.
What should be fixed:
1) Swearing fealty should be available only to your de iure liege as is the case for kingdoms.
2) Being able to ask other vassals to join your faction war even though they were not part of your faction seems a bit OP to me.