Radical Muslims are all Sunnis, at least that is what Muslims claim.
The origins of radical Islam in recent times began in Egypt in the 1950's,and then was bolstered when former Saudi religious police were sent to Afghanistan to combat the Russians. Saudi Arabian are Sunnis and Wahhabbis and the Saudi government sends a lot of missionaries to both Muslim and non-Muslim countries to proselytize. There are the Saudi government- supported Wahhabbi converts as well as Talibanis who are mostly Pashtuns converted to Wahhabbism in the 1970's and 1980's
Shias do not do this: they do not send missionaries, though they do send money to Hezbollah in Lebanon to piss off the Israelis.It is pretty certain that if they were really as badass as the Israelis claimed, they would be sending materials to make much more accurate rockets.
Americans include Iranian mullahs as radical, because they are anti-Israel.
The people who want to build the Community Center in NYC at Park 51 are Sunnis of the Sufi sect. The Sufis are the mystics of Islam and have never been violent.