It's A
Irrigation was overused, the soil didn't get any rest (crop rotation is a younger invention), the result was salinization of the soil, which led to decline of Sumer.
Answer:
Nativism: protecting those who are already inhabiting and existing in an area against newcomers or immagrants
Examples:
Chinese Exclusion Act
Immigration Resctriction League
He launched Operation Linebacker. He bombed Hanoi and Haiphong that led to the
destruction of the North’s economic and industrial centers. He continued the bombings and also threatened to withdraw U.S. and end the agreement. Nixon halted the bombings and signed the
Paris Peace Accord that ended U.S. involvement in the area.
