In 1895, members of the Gloucestershire Engineer Volunteers reenacted their famous stand at Rorke's Drift, 18 years earlier. 25 British soldiers beat back the attack of 75 Zulus at the Grand Military Fete at the Cheltenham Winter Gardens. Veterans of the American Civil War recreated battles as a way to remember their fallen comrades and to teach others what the war was all about. The Great Reunion of 1913, celebrating the 50th anniversary of the Battle of Gettysburg, was attended by more than 50,000 Union and Confederate veterans, and included reenactments of elements of the battle, including Pickett's Charge. During the early twentieth century, historical reenactment became very popular in Russia with reenactments of the Siege of Sevastopol  , the Battle of Borodino  in St Petersburg and the Taking of Azov  in Voronezh in 1918. In 1920, there was a reenactment of the 1917 Storming of the Winter Palace on the third anniversary of the event. This reenactment inspired the scenes in Sergei Eisenstein's film October: Ten Days That Shook the World. Large scale reenactments began to be regularly held at the Royal Tournament, Aldershot Tattoo in the 1920s and 30s. A spectacular recreation of the Siege of Namur, an important military engagement of the Nine Years' War, was staged in 1934 as part of 6-day long show. In America, modern reenacting is thought to have begun during the 1961-1965 Civil War Centennial commemorations. After more than 6,000 reenactors participated in a 125th anniversary event near the original Manassas battlefield, reenacting grew in popularity during the late 1980s and 1990s, and there are today over a hundred Civil War reenactments held each year throughout the country.
Answer this question: How many years did Civil War Centennial commemorations occur?
4