Why did the United States expand it's role in the pacific?

United States wanted to expand the role because:

1-military: United States wanted to have a base that could be used as millitary base to stock fuel and supply.

2-trade: More control in Pacific Region would give US more opportunity to trade with other nations (mainly in Asian continent)

3 - industry: Due to the international relation, it would lead to industries in US able to obtain many cheaper resources and workers.