To militate against something means to make it less possible or likely. To militate against someone means to prevent them from achieving something.
例句
Her background militates against her...她的背景對她不利。We can never promise to sail anywhere in particular, because the weather might militate against it.天有不測風云，所以我們永遠都無法保證會航行到哪個地方。
英英詞典釋義
Verb
1. have force or influence; bring about an effect or change;
"Politeness militated against this opinion being expressed"