英文文法一問，點解...to contribute to maintaining peace ... maintain係加ing?

to contribute to + noun/pronoun
The fair weather contributed to the success of the expedition.
促成／貢獻
To contribute to maintaining peace among nations is every man's responsibility.
= It is every man's responsibility to contribute to maintaining peace among nations.

maintaining peace among nations是「動名詞片語」(gerund phrase)，當作前面介系詞to的「受詞」。
不定詞不能當介系詞的受詞，所以本句的maintaining ...不能換作to maintain。