If you're in southeast asia the calculus changes. But the cost benefit analysis really leans against annexing hostile locals these days unless it's some nationalist mythology like China and Taiwan. And if you're in southeast asia I'd say future heat waves and climate disasters means you'll be more likely heading north into China than them heading south.

If it's a soft ideological takeover you're envisioning then that's really the responsibility of the democratic society you live in. Democracy falls when people no longer believe in its ideas or that it is an effective way of governance.