Although this text is non-fiction, much of it is told
like a story. What is the author's most likely purpose
for writing the text in this way?

The texts can be told like a story to give them more credence and not to be too confessional.

Explanation:

Often life narratives are written likes stories because of how much stories and their format effect how we understand the content.

While in the autobiographic narration people do care more about the facts that are being told, in a story format people understand the larger idea behind the text without being told it.

As such they also retain that larger idea for a longer time and are able to contend with it for much longer.

This one can see is a good reason for such usage.

b. the colonies must seek protection from other nations.