Why did Osama Bin Laden declare a holy war?

Answer 1

Bin Laden declared a holy war because he believed the United States was unjust and tyrannical.

Answer 2

Osama bin Laden declared a holy war, or jihad, because he believed it was a religious duty to defend and protect Muslim lands that he perceived as under attack or occupation by non-Muslim forces, specifically the United States and its allies. He was seeking to mobilize Muslims worldwide to join his cause and fight against what he viewed as oppression and injustice.