瓦解 (wǎ jiě) means 'to disintegrate, collapse' — it describes a gradual breakdown from within, like an organization, system, or morale falling apart piece by piece. It is less sudden than 崩溃 (bēng kuì, violent collapse) and more figurative than 垮 (kuǎ, physical or structural collapse). 解体 (jiě tǐ) is a close synonym but is more formal and often used for political or organizational dissolution.