If you know nothing about them, Giuseppe Garibaldi and Giuseppe Mazzini were two important personalities of the Risorgimento, the period and process that led to the independence of Italy and its birth as an independent country during the 19th century. Mazzini founded and inspired several movements committed to the independence of Italy, and his idea of Italy as a republic ended up being prophetic; Garibaldi was more the kind of action guy, attracting a lot of volunteers that fought with him on the battlefields against the foreign armies. Two patriots, two different personalities, that acted on different aspects with different methods but for the same purpose. In short, the right material for a good buddy movie! :D
There is no particolar reason for the choice of trolls instead of other kind of monsters... actually trolls aren't even part of the traditional mythology of Italy, but whatever, they were easy to draw. Enjoy.