Byzantium/Constantinople was conquered in 1451, but the empire continued to decline starting around the 18th or 19th centuries. It officially died in WWI. As for how long it was a major threat to Europe, the empire's prime was the 16th century, under Suleiman the Magnificent.
An idea for a bill can come from anybody, however only Members of Congress can introduce a bill during Congress. So True.
Western political though simply refers to the culminaton of ideas that can be found in Europe and the US + Canada. All of these three entities tend to take the same or similar stance towards different political aspects of life.
