Season 1: American Revolution
Season 2 (Really just a mini season bc of lack of characters): American Civil War
Season 3: WW1
Season 4: WW2
Season 4 Part 1: European Campaign
Season 4 Part 2: Pacific Campaign
Season 5: Cold War

Main Villains:
Season 1: British Empire
Season 2: CSA
Season 3: German Empire, Austria-Hungary, & Ottoman Empire
Season 4 Part 1: Third Reich
Season 4 Part 2: Japanese Empire
Season 5: Soviet Union, China, Cuba, North Korea, Vietnam, & other communistic countries