I've read a little bit about the causes of WW1 and WW2, and each account I read mentions the US very little if at all. This seems fair because the US more or less did its best to stay out of either World War until it became apparent that they couldn't.
Could we say the US had no role in the outbreak of either war though? Could we say US non-involvement itself was a cause?
Nothing I have ever read has indicated that the United States had even the smallest involvement in the outbreak of the First World War. It was a wholly European affair initially that was caused by the entangled web of alliances, treaties, envy over colonial possessions and unchecked military buildup. If anything, some European powers may have viewed the rise of a new power such as the United States with jealousy as in the space of some 140 years the US was already establishing itself as an economic powerhouse and had several colonial possessions of its own. To say that this had an influence on the outbreak of war however would be a stretch.