After the fracture of the Roman Empire in 285 CE, this civilization was divided into two territories: The Western Roman Empire based in Milan and The Eastern Roman Empire based in Nicomedia. However, due to the fall of the Western Empire in 324, the Eastern part decided to shift its capital to Constantinople, which is nowadays known as Istanbul. This was home to the Roman emperor until the fall of the city at the hand's of the Ottoman Empire in 1453.
The main thing that the AEF, doughboys, and harlem hellfighters (369th regiment), have all in common is that they were part of the "American Expeditionary Forces," who were sent to Europe in 1917.
After WWII Europe was divided into a US-led Western Bloc and a Soviet-led Eastern Bloc. Internationally, alliances with the two blocs gradually shifted, with some nations trying to stay out of the Cold War through the Non-Aligned Movement.