This might be a stupid question, but I was wondering why it is necessary for the merge sort algorithm to divide the list into two and mergesort each partition before merging all of these partitions into a sorted list as this animation shows:

<http://www.ee.ryerson.ca/~courses/coe428/sorting/mergesort.html>

It seems that near the end of the mergesort algorithm when it reaches phase where it merges the two large arrays together, why not just do that in the first place? I don't see why it is necessary to mergesort every part of the array while it seems that the algorithm could just divide the entire list into two and merge them together in a sorted array on the first step.

Am I missing something here?