That's actually a valid question Trump ask on the Civil War. Why couldn't it have been avoided? That's pretty close to being a rhetorical question as, to state the obvious, it could have been avoided.
The U.S. With its many sovereign States, diverse geography and diverse peoples has had a political genius for compromise that has held us together as a nation. The Civil War is an example where that genius failed our nation completely as many compromises were available that could have prevented the war.
It's probably a fair assumption that Trumps view on Jackson and the Civil War is based on how Jackson handled the nullification crises. However there are some major differences between the nullification crises and the Civil War.
The cause of the nullification crises was tariffs. The cause of the Civil War was slavery, or more correctly, slavery expanding into the territories. Both were sectional disagreements. The tariffs that precipitated the nullification were intended to protect the nations developing industry, which it did, but it also harmed agriculture exports in the South. Having said that the tariffs were only opposed by half the Southern States.
On the other hand the abolition of slavery in the South at that time would have represented the largest transfer of property in human history as slaves represented a very large proportion of Southern wealth. It's unlikely that the Southern States would have simply given up that wealth.
In short the abolition of slavery, which was the cause of the Civil War, was a vastly larger political issue than tariffs and had Jackson tried a similar approach with the slavery issue it would have guaranteed war.
So in that respect Trump is wrong but Jackson's handling of the nullification crises in his time probably did prevent war.