I've been reading a couple of American Civil War posts on this sub recently and it was mentioned a couple of times that Napoleon III was doing something in Mexico. I had never heard of this before, care to elaborate?
Napoleon III was supporting a Habsburg candidate as Emperor of Mexico. Mexico was undergoing upheaval and the powerful conservative elite, mostly estate owners, promoted the idea of a European aristocrat being elevated to emperorship of Mexico. They approached the Habsburg, who used to rule Mexico when it was part of New Spain.
Napoleon III wanted to create a puppet state in Mexico, which was aligned with his religiously conservative wife's wishes. Ergo, Maximillian accepted the offer despite initial hesitation. France wanted access to American markets and mines.
Napoleon III's casus belli was debt owed by Mexico to three European powers: France, Britain, Spain. All three sent ships and troops in 1863, but France sent a large contingent intending to stay and control Mexico, thus the other two withdrew. Maximilian was married to Charlotte of Belgium who is of the French Orleanist family, and that couple was considered a suitable puppet figurehead by the French.