How did mapuche lose their land?

Answer 1

Well the Chilean government took it away from them because the Spanish conquistadors couldn't do it for 300 years.

The Spanish that came to Chile fought hard against the Mapuche but they held, even they gave the Spanish some nasty defeats. The Spanish could never beat the Mapuches that's why, during the Spanish rule, the Kingdom of Chile ended in the Bío-Bío river because crossing that you would be entering Mapuche territory.

At the end of the XIX century, the Mapuche were very weakened for several reasons so the Chilean government managed to get in the territory and claim it as theirs although even to this day, some communities still protest and fight against the police to get their lands back.