From ky understanding he just wants to ensure that all his comrades didn't die for nothing and that his people's traditions and religion are kept intact.
And unfortuantly for him to be in the place to ne able to realistically do that, he has to be in a seat of power....basically at the top.
Ive always got the impression of the flame alchemist when I see ulfric from fma. Both have done terrible things and have still done terrible things like creat civil wars all for the greater good of the country.
Thats just my opionion and people have the right to disagree though.