What is the impact of massive immigration to America and Oceania?

Immigration is a double-edged sword, both good and bad!

The good side is to promote cultural exchanges, economic development and humanistic progress among all ethnic groups!

On the bad side, it destroyed the local cultural environment (Europeans entered America, which can be seen in the destruction of Indians), broke the balance of the local environment and competed with local people for resources (once controversial mainland pregnant women went to Hong Kong to give birth, which can be seen in the competition for local hospitals and other resources)!