Age of Nationalism (AoN) is a modification of Europa Universalis 2 that has a timeframe of 1820-1914. The mod was created by Paradox Forum members Stjaba and Styrbiorn with the contributions of a few others. Unfortunately, because the staff was so small, with Styrbiorn doing the vast majority of all the coding, the project was never completed and remains permanently in beta form. Nevertheless, beta AoN was very entertaining and filled the need for a 19th Century EU2 game until Victoria came along.
With the release of several new patches since work on AoN ceased, to run AoN on the latest version of Eu2 would require editing. If you want to play the AoN, it's probably best to run 1.06 or 1.07 Eu2. Fortunately, many of the edits and files of AoN were incorporated by Hive into the mod Age of Imperialism (Europa Universalis II) so it's possible to play into the 19th century under the latest version of EU2.