Imran khan had been raising the issue of election rigging from day one, he has told government, election commission and Supreme Court to audit the election but neither government nor Supreme Court is taking any action against these riggings. So after so much struggle he finally decided to go for long march to protest against these rigging.
And secondly Imran khan is bringing army is because they can act as the neutral umpire and can give a justice to all without any polarity.
And at last the people in his long march protest are indeed in millions and it would have been more if nawaz sharif would not have sealed the whole city by containers.