KanjiJLPT N1
Thwart

thwart, separate from, prevent, obstruct, deter, impede

Mnemonic

A village perched high above deadly stairs uses them to thwart every invader. The stairs are treacherously steep and crumbling—anyone who tries to climb them tumbles back down. The village remains unconquered precisely because those stairs block all who approach.
Additional thoughts
Picture a fortress-village atop a cliff with impossibly steep, broken stairs. The stairs ARE the defense—no wall needed. Stairs = obstruction = thwart.
Quick recall
A village atop crumbling stairs thwarts every attacker who dares climb.

Details

The keyword for 阻 is thwart. This kanji conveys the idea of blocking, obstructing, or preventing something from proceeding as intended. It carries a strong sense of standing in the way of progress or hindering an action, much like placing a barrier that stops forward movement. The character is commonly associated with resistance, impediment, and the act of foiling plans or efforts.
On'yomi
Kun'yomi
はば.む