What is on of the causes of mechanical weathering? acid rain
oxidation
animal actions
carbon dioxide

Mechanical weathering is weathering caused by the breaking down of rocks by physical force without any change in the chemical nature of the rocks. Mechanical weathering is usually caused by extreme hot and cold temperatures. Water seeps into cracks in rocks, freezes, and expands, causing the further breakdown of rocks.

Explanation:

the only other powers were germany russia and uk and they were too busy fighting each other wearing each other down   that the us was becoming strong and they were becoming weaker