The EU came into being to stop future wars and to establish a long lasting relationship based on mutual aid and trust. Before the EU France and Germany fought like 3 wars while they had open economies and free trade. You can't just nitpick parts of history to suite your agenda.

you obviously can also see how nations arent really going about outright annexing nations with impunity, right?

Why are you now changing the goalpost to annexation while you first stared to talk about war in general? Britain (a Liberal empire) had no problem with waging war against China to establish free trade routes into China while the Chinese emperor tried to restrict their influence in the region.