Forced migration can occur due to the following reasons:
- Political regime preference - Individuals may be forced to migrate due to oppressive political regimes or conflicts.
- Environmental disaster - Natural disasters such as floods, earthquakes, or climate change can displace communities and force migration.
The other two options, "higher living standards" and "greater employment opportunities," typically relate to voluntary migration rather than forced migration.
So, the correct answers are political regime preference and environmental disaster.