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- Military: Getting troops to take control of enemy territory. Often a state invades another to start a war, but invasions can happen anytime during war.
- Others: Sometimes, biologists speak about an invasive species. There might be locust swarms invading, or that some algae spread far more rapidly in new territory.
One of many examples is the importing of rabbits to Australia. As they had no enemies, they did what rabbits do best. They multiplied. To get rid of them, people then thought about importing foxes as well.