I like to consider myself a pretty egalitarian fan when it comes to international soccer.
What I mean is, besides the USMNT, I root for a wide variety of teams. Of the 32 teams in this year's competition, I would be happy with four or five winning the whole thing, and I wouldn't mind an additional seventeen or eighteen performing well. In a game where I have no distinct loyalty, I tend to answer the question of "Who am I pulling for?" by answering an even easier question: "Who do I hate more?"
The rubric for who I hate is fairly ephemeral. It could be something to do with world history, it could be something to do with a single player being kind of a dick. For example, in the Group H match between Chile and Switzerland, I'll probably root for Chile because A) Spanish is better than French or German, and B) let's face it, the Swiss are kind of a bunch of pussies. It's not a scientific process, but it's actually pretty consistent.