So my playthrough as Date..

[Trunting]

So started a game as Date (before that I already tried to play as kokujin of Ibaraki, but soon I realized you can't do anything as such). I annexed the small province in the south of Date, but then I was outwiped in a war with Mogami. Despite them having 3 provinces and me 5, they were able to raise more men than my levy consisted of. And during the war, they were able to instantly raise like a 1000 men again. What am I doing wrong?

 

[Trunting]

So I started a new game as Nanbu. This time I was able to annex all major starting opponents, but when I finally conquered Osaki Clan, soon afterwards Uesugi declared war on me and it looks again like a game over. My question: How to fight opponents, who are double the size of yourself?

 

[Yakdast]

I am happy to see some people still play that game

 

[MJWilliams]

Not played this game in a long time (despite rating it very highly) As I recall your best bet against blobs like Uesugi is either spam upgrade your castles for huge levies and/or get as many retainer units as you can. Worth exchanging hostages with them and marrying them too for security until you're strong enough.

Another option would be the "plot to attack" option via intrigue. If you can convince enough smaller clans to join, you can strike with what is effectively a huge coalition and overwhelm them. The AI reluctancy to sign peace in this game means between yourself and your cohorts you can make huge land-grabs.