When Annabeth was attacked by the Manticore, they both got thrown over a cliff's edge during a skirmish. She was caught by Luke and the General who was known as the person working closely with Kronos. Artemis later explains how she tried to save the people but she couldn't save Annabeth but she urges other gods to help them.
It started with the Chinese Exclusion Act of 1882, but 10 years later it then came to the US opening Ellis Island in which immigrates had spent time before being able to actually enter the US.
I would say it has to be trade
