While Thanos and Kang the Conqueror may be major villains in the Marvel Universe, their tactics are very different, as shown in how they took on the Inhuman king Black Bolt.
Blackagar Boltagon is one of Marvel's most underrated heroes when it comes to the damage he can cause simply by speaking a single word. Black Bolt's Inhuman powers mean that even when he whispers, his voice unleashes a powerful attack that can take down even powerhouse superhumans. However, Black Bolt barely ever speaks with his actual voice, as even the slightest noise produced from his mouth can cause serious devastation. Thanos and Kang the Conqueror both came up with unique ways to take on Black Bolt and his mighty scream, showing the differences between how the two comic book villains operate when facing a worthy opponent.
Thanos and Kang the Conqueror's approach to dealing with Black Bolt reveals the key difference between the villains. The Mad Titan took on the royal Inhuman in Infinity #4 by Jonathan Hickman, Jerome Opena, Dustin Weaver, Justin Ponsor, and Chris Eliopoulos. With Thanos searching for his son Thane, he fights Black Bolt to seek information on his Inhuman offspring. However, when Black Bolt uses his powerful voice against Thanos, the villain takes the blow head-on, as he keeps fighting despite the attack destroying his armor.
In The Uncanny Inhumans #0 by Charles Soule, Steve McNiven, Jay Leisten, Justin Ponsor, and VC's Clayton Cowles, Kang the Conqueror takes the opposite route. After Black Bolt assaults his fortress, Kang opens a portal which transports the blast back in time, causing a major disaster. He then threatens that if Blackagar raises his voice again, he'll send the shockwave back to the hero's birth, killing him and his family.
Ultimately, the two villains' different ways of dealing with Black Bolt showcase what makes each so dangerous. Thanos has no regard for his own well-being, and uses his immense strength and power to accept the damage from Black Bolt's scream and fight on. Thanos has long been one to settle his own problems, and risking everything in a direct confrontation just for the joy of winning is very much his style. In contrast, Kang the Conqueror is cunning and creative, prone to misdirection and manipulation rather than direct assault. While Thanos would rather kill an enemy with his hands around their neck, Kang is the sort of villain who delights in the idea of using their own attack to end their life.
Both Thanos and Kang are dangerous and deeply evil individuals who qualify as geniuses, but given the choice, the Mad Titan prefers the direct approach, while Kang loves nothing more than a convoluted scheme that leaves him on top. Faced with an enemy of Black Bolt's incredible power, both villains default to their standard tactics, revealing the truth of who they really are. It's because of the tactics seen in their encounters with Black Bolt that each has been so dangerous to the Avengers on different occasions, with an attack by Thanos often beginning with a huge fleet approaching Earth, while an attack by Kang is only detectable once the trap has already closed.