That's a question for another thread, but to keep it short.Curious as to why such a large number of threads have to do with downfall of Ottomans (Byzantine wank), a successful Confederacy, or a destruction of Mexico.
1. The Byzantine Empire is one of the most popular polities there, so a restoration of the "heirs of Rome" has a great appeal on the amateur (or even professional) history lover. Since the Ottomans were the ultimate nemesis of the Byzzies the antagonism is simply inevitable.
2. The ACW was the largest conflict in American soil and most of the userbase there are Americans, since the CSA were the losers the main point of interest of WI scenarios, after all "WI: the Union faster faster!" as simply boring.
3. Mexico was one of the most unfortunate victims of American expansionism, so devouring more of Mexico is a goal for most Americo-wankers, curious of why you picked Mexico over Canada (which is annexed more often than not).