Why do you the Japanese changed their approach from trying to win the support of the colonized people's to acting as conquerors

OK ...

So,

1) Japan is an island and they didn't have enough resource. Winning the support of the people takes more time. So, they thought a faster way to gain raw materials and resources was by conquering the other lands. Also, they thought using force was faster and effective.

2) To spread fear among other countries so that they wouldn't oppose Japan