For the most part, the bias against Wikipedia as a source is mostly related to a few overblown incidents and just bias against new internet based sources from old-fashioned professors. For the most part, the sources they use are valid, and its moderated heavily enough to fix most errors. If your teacher/professor doesn't like it though, I wouldn't use it.
As for the US Military, we would crush South America with a full, drafted army. We have such a massive air and naval superiority over them, that it just wouldn't matter how many men they have. If they have no air cover, all they can do is hide in a jungle or cave as bombs and cruise missles rain on them. And since the US probably wouldn't be looking into being an occupying force in the situation, hiding gives them no benefit besides survival. No country can match our air force and navy in a one on one conventional conflict. Not even debateble. China has a lot of sheer numbers, but their Navy is flimsy and their Air Force for the most part, is a lot of old Soviet fighters that aren't even as good as our current stuff, much less the new stuff coming down the tubes like the Raptor and F35.