Historians often use a. d. 476 to mark the end of the western roman empire. why

In AD 476, Emperor Rolulus Augustulus, at 14 years old, was the ruler of the Western Roman Empire. During this time a Germanic general named Ocoacer overthrew the emperor. This was the last time an emperor ruled over Rome which is why historian consider this year the end to the Western Roman empire.

They had to go back and forth to the atlantic ocean and the pacific ocean to build the panama canal thats the best i can answer