There are multiple types of boundaries, all of them being set by the humans, some following some natural features, some not. Some of the types of boundaries are the natural boundaries, geometric boundaries, and maritime boundaries.
The natural boundaries are set long a natural feature, like a river or a mountain chain. Examples of this type of boundaries are the boundaries between the USA and Mexico along the Rio Grande river, or the border between Macedonia and Greece along the Kozhuf and Nidze mountain ranges.
The geometric boundaries are usually set in places that are very sparsely populated, mostly in desert areas. We can see this type of boundary between Libya and Algeria.
The maritime boundaries are boundaries set on ocean/sea waters between an island nation and continental nation, or between two island nations. An example of this type of boundary is the maritime boundary between Japan and South Korea in the Japanese Sea.
Immigration to the north provided workers for production and replacements for soldiers killed or wounded.
