Yes.

A few caceats:

IF we have to have countries and arbitrary borders, THEN if another force decides to invade for whatever reason, a war to expel the invasion is justified, but only if the people in the invaded country deem it worthy to fight and possibly die in defense of their country.

Invasion is never warranted.

Countries are pretty gross. I detest all forms of government except self-government (meaning individual humans governing themselves).