Answer:
Slavery and Many travelers lost their way.
Step-by-step explanation:
The target of The western Expansion was the ex-Louisiana territory that's previously owned by France before being bought by United States.
Many states fight over whether the new western territory should be considered as slaves states (where slavery is allowed) or free states (where slavery is illegal.
On top of that, the navigation technology among settlers were still somewhat primitive. So, when they embarked on a journey from Eastern States to Western states, many of them actually lost their way and ended up settling in Midwest or Southern part of United States.