The Victoria 2 Historical Project Mod is an attempt to improve the game Victoria 2: A Heart of Darkness without changing the base game experience too much. Built using parts of the mods NNM and PDM as a base, the main aim is to improve the historicity of the game, including countries, map and pops and to add more historical flavor to the game, while taking into account the plausible historical outcomes and the mod performance. The first release includes a vastly improved country composition and a complete rework of the global slave population. Most countries now have slavery and slaves and the historical number of slaves, as well as their pop composition and religion, was used when available. Future releases plans are to include a serf pop type and reforms to represent it, other meaningful reforms for the time era, dynamic soundtrack for countries/governments/regions and a 1816 (or 1815) start date.
Another one, this one was my mistake. A few of the assimilation modifiers were grouped and this in turn made pops assimilate when they shouldn't. Here's another update to fix that. The Checksum is JRLI. The update is compatible with version 0.3.8.x. Changelog in the full description.