How did China, Brazil, Kazahkstan, and Russia gain such crooked borders (ancient, Chinese)

[NJ Brazen_3133]

How did large countries that border multiple other states end up with such crooked borders?

Look at Brazil. How is was the border with its northern neighbors created? It is kind of goes up and down, up and down. As it heads south into Peru, Bolivia, and finally Uruguay it zigzags.

As for Russia and Kazakhstan, how did they determine who gets the Caspian Sea. Heck, if I was a soviet leader, I probably would have taken the Caspian, Aral, and Lake Balkhash, and just let the Kazahks have everything in between. Afterall, they are most pastoral herders right?

How did the Chinese inland borders form? You have inner Mongolia which actually has more nomads than Mongolia proper, so why not just take even more land north then? And why is it so crooked?

[B. Rago]

The oldest way to determine the boarder between two regions is by using a geographic feature, like a mountain range or a river.

The boarder between Brasil and Bolívia is an imaginary line conecting rivers Madeira and the springs of Javari.

The boarder between Barsil and Argentina follows the rivers Iguaçu (from the "Cataratas do Iguaçu", or "Iguazú"), Santo Antônio, Peperi Guassu and Uruguai, until the mouth of Quaraí.

The northern frontiers of Brasil are settled by watersheds, such as the boarder Brasil-Guiana, defined by Serra Acari, ending at Mount Roraima, where the boarder Brasil-Venezuela begins.

That's the main way to define boarders in the History of the world, the straight American limits that are weird... Probably those other countries have crooked boarders because their boarders are landmarks too, or they have incorporated regions that had rivers and ranges as ancient boarders...

[MalaMan]

Borders are usually determined based on rivers and mountains...