Guru arjan was the first to die at the hands of the mughul sultan, jahangir. Most historians agree that the Mughal sultan saw the sikh popularity in the western part of his empire as a threat tk his rule and had guru arjan brought to him and told him to either convert to Islam or be executed. And guru arjan gladly chose death over forced conversion.
After this incident the Sikhs became more martial and also hostile to Muslim rule, this eventually lead to the sikh rebellion when guru har gobind helped the kashmiri pandits and protected them from mughul persecution and their atrocities against them. For this Aurenzeb had him executed. He was killed because he chose to protect and defend the innocent against mughal sultan. After his execution, the Sikhs rebelled again.
Brother please learn history.