Imam had realized that he has to make the ultimate sacrifice to trigger a massive awakening within the Ummah against the Zulm of the tyrants of the time. The only option he had was to present himself for a sacrifice which would violently shake the collective conscious of the Ummah at that time to wake up and rise. An extremely difficult choice but the decision was taken deliberately. The results of his decision was exactly as he had planned. The whole Ummah woke up after the sacrifice at Karbala. 

Islam Zinda hota hai har karbala key baad ! 

Karbala is NOT a Shia Sunni issue. It is a principled stand of ahl beyt against Taghoot, Kufr and zulm of the time. 

Now here is the ultimate message: 

Being a follower of Imam means that you make a stand against Zulm, Kufr and Taghoot of the time. Else, you are either a "Koofi" or a "Yazeedi" or part of the "sleeping Ummah" BUT definitly NOT part of Hussaini Caravan. Karbala is NOT an event. It is a Phenomenon, a lifestyle, a way to live with dignity and die with honor !