Dangers and threats, loss of control, losing an advantage, duty and responsibility, increased pressure and ticking clocks

Fleeing to safety and stability amid a political, humanitarian, or economic crisis
Marrying someone who lives far away
Being sold, kidnapped, or trafficked
Attending a school away from home
Accepting a distant job opportunity 
Pursuing diplomatic or missionary work
A natural disaster making the character's home or homeland unlivable 
Having to seek critical medical care in another location
Receiving serious and credible threats that push the character to start over elsewhere
Relocating to take care of an ill family member 

Getting used to a new routine
Having to learn a new language
Needing to establish new relationships
Having to find a new form of employment
Getting lost
Having a different socioeconomic or social status than before
The character's children having to change school
Having to leave belongings behind
Not knowing cultural norms for the new location
Not being able to attend school because the new situation doesn't allow it
Unintentionally offending someone
Having to find housing 
Needing to leave a pet behind
The character's professional credentials not being recognized in the new location
Having to find new businesses or service providers 
Being cut off from support
Not knowing who to trust just yet (or feeling there's no one to trust)
Being unable to communicate with those left behind