The petrodollar is an interesting theory, but I have strong doubts about it. Global dollar-denominated oil trade is a tiny drop in the bucket of global dollar-denominated trade - not a sacred cornerstone that must be protected.

Geo-political power games (Gulf War I) and outright stupidity (Gulf War II) seem like the more likely catalysts for the Iraq war (And you noted a few of the causes of the Libyan one).