All of this totally new to me (despite a decent education). Readers in too much of a hurry to spend time on a video may choose instead to browse this article at Latvian History:
The four Latvian tribes differed from each other in many ways. The Semigallians are said to be mightiest Latvian warriors. That could be true because Semigallians resisted to crusader invasion longer than others did. The Latgalian kings were the richest rulers of Latvian tribes. The wooden fortress and city of Jersika was a large and proud center in Latgale. The last ruler of Jersika Visvaldis is one of the legendary ancient kings of Latvia. But the Curonians are seen as the great sailors and raiders.Or this post about the Curonians versus the Crusaders.
A tip of my blogging cap to reader Alexsejs for providing the links.