The Dai Li were a group of secret police and elite royal protection force that were based in Ba Sing Se, the capital of the Earth Kingdom. The Dai Li were originally made by Avatar Kyoshi but she later mentioned that she regretted making them due to how susceptible they may have been to corruption. The Dai Li specialized in interrogation and protection duties.
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A Lethal Protection Force
The Dai Li forces were far more skilled and power than most of the Fire Nation's military units. Even the Intel Troopers feared the Dai Li. Their title was more prestigious than the Earth Kingdom Commandos who they were domestic rivals with. Unlike the Dai Li, the Earth Kingdom Commandos were loyal to the Fire Nation Army and Generals rather than political or security leaders. They answered directly to the Grand Secretariat of Ba Sing Se.
Unlike the Earth Kingdom Commandos, the Dai Li were made up entirely of earthbenders.
Coup of Ba Sing Se
Azula infiltrated Ba Sing Se taking Kyoshi warrior uniforms that she stole. She gained the loyalty of the agents and used them to overthrow Long Feng and place the Earth King on house arrest. This event caused greater distrust among Earth Kingdom Commandos and Dai Li agents. Three squads of Earth Kingdom Commandos would later attempt to assassinate Azula but Azula and her Dai Li agents managed to defeat them.
Other commandos still served and worked to undermine the Fire Nation forces of the Earth Kingdom until Aang and the White Lotus managed to topple them.
Difference in roles
The Earth Kingdom commandos had a different role. They focused more on recon missions, assassinations, and strategic attacks on valuable military targets rather than defense duties. The times they had bodyguard duties they were protecting or accompanying army officers that were carrying out attacks on their enemies. While the Dai Li always stayed within the borders of Ba Sing Se or other essential Earth Kingdom areas of importance.