These are based on Paul Spring's reverse civil war thread
Birth of a Nation--Good 4-hour movie about the events that led to the founding of the Republic of New England after the 1857-1861 war. However, this does touch upon the invasion of northern Mexico and the Yucatan by Mexico in 1859, which helped New England win independence in 1861. (New England is made up of New York, Vermont, Massachusetts, New Hampshire, Maine, Connecticut, Rhode Island, Pennsylvania, New Jersey, and Ohio.)
Grapes of Wrath--The follow up to Birth of a Nation, this details the Mexican invasion of the U.S. and the Yucatan, which led, in 1861, to victory for New England. However, as this movie shows, it was the beginning of the end for Mexico, as the U.S. defeated it by 1864 and annexed it, beginning a series of events that exploded 80 years later.
Enemy at the Gates--The true account of the Battle of New York between the Republic of New England and Britain on one side, and the U.S. on the other, during the Second Great War (which Britain, Germany, Japan and New England won against France, Italy, the Russian empire, and the U.S.) from 1941-1946. Over 8 million people were killed or wounded during this, the bloodiest battle of the Second Great War, on both sides during the battle, and New York was left in ruins.