Within a single region using multiple AZs, you survive a burning data center. But what if an entire region—say us-east-1—fails? The major us-east-1 S3 outage in 2017, the us-east-1 Kinesis/API failures in 2021—these happen rarely but really. Multi-region architecture answers the "entire region disappears" scenario. Yet the moment you cross regions, physics intrudes: the speed of light. Round-trip latency between Seoul and Virginia exceeds 200ms, making synchronous replication (possible in single-region millisecond timescales) essentially impossible across regions