I see a lot of people saying "It's a game about war, delaying it for the situation that is happening in Ukraine is silly because there's a lot of war games coming out." While that is true, that is kind of missing the forest for the trees.
Advance Wars 1 literally begins with you
taking back territory conquered by the Blue Moon army after an invasion which is led by a character (Olaf) that
very obviously is based on Russian characteristics.
I don't know if there's been any developers confirming this but for what it's worth, the Advance Wars Wiki also mentions the following:
"Blue Moon is modeled after the real world nation of Russia, as well as the Soviet Union."
I think the delay makes sense and is in line with previous decisions Nintendo has made.