A historian who compares events in North America to events in South America is organizing history by

Like geographical identification, history can be determined based on religion, periods, description, commercial, and learning. One can state in a more comprehensive judgment that all the knowledge of the past events comes beneath history. A region is a stretch of land that has traditional characteristics. A region can be explained by physical or man-made characteristics. In the comparable means when A archaeologist who connects developments within North America to developments in South America is establishing history by regions.

A historian who compares events in North America to events in South America is organizing history by Region. The North America and South America are two regions and comparing their events simply means historian is organizing history by Region.

Likewise if historian compares two cultures, he/she is organizing history by cultures.