External pressure can lead to the relatively abrupt end of a civilization (and, often, the adoption of another).
The clearest example of external pressure on a civilization is foreign invasion or sustainedwarfare. Protecting a civilization’s borders can be extremely expensive and demand a strong military at the expense of developing or maintaining other aspects of a civilization. External pressure can lead to the relatively abrupt end of a civilization (and, often, the adoption of another). The fall of the Aztec Empire with the arrival of European conquistadores is such an example.