"Liberalism" has always stopped at the water's edge. So-called conservatives and liberals have always agreed on war. It used to be called our "bipartisan foreign policy". When the Iraq and Afghanistan wars were being financed by supplemental appropriations, outside of the defense budget, I followed Oregon's senators' and representatives' votes on the supplementals. More often than not, Rep. Peter Defazio voted for the supplementals, and he is supposedly a "liberal". 

Both Democrats and Republicans are responsible for our wars, as is most of the public, which just ignores them. The middle class ignores the wars because it isn't their kids who are fighting in them, it's mostly working-class kids for which the US now has no economic function, so they're expendable. Not enough people care to stop the wars, so they go on, killing people and wasting trillions of our tax dollars.