I propose adding a "Preferred War Type" option to account options or military/nation customization.
This will help to ease declaring war and make it a more seamless experience for users without having to use the dropdown menu unless they want a war type other than their preferred one.
Often in wars, there is time pressure to declare in a blitz and the current dropdown menu doesn't stand out well in the current UI.
I don't believe this should require too much work on the development side, and it'd make declaring war easier, which is half the game and in the name.