Loosely speaking, probably not right now. A lot of countries avoid war because they are worried about the potential response from the United States. With an isolationist-focused US that isn't the dominant military power (in order for the US to not be the dominant power it'll have to undertake more isolationist tendencies like reducing military spending) there's nothing to fear from invading your neighbor.
But this is just an examination of practical reality. Ideally we wouldn't have a hegemon. Ideally maybe we wouldn't have countries either.
But this is just an examination of practical reality. Ideally we wouldn't have a hegemon. Ideally maybe we wouldn't have countries either.