Anyone interested in the difference between Sunni Islam and Shia Islam, and why that matters in the current situation.Here it is .

Sunni Islam is the older, more pure form. It has three principles: 1. There's only one God(the same God of all Abrahamian religions) 2. Muhammad is God's prophet(as were Jesus, Moses, et al) 3. Life after death Shia, while believing in all three, add more: 4. Justice 5. Imams after the prophet(12,7,6 depending on the sect)

This has serious implications. Shia, being the new one, see the Sunni religion as a bit incomplete, backward. Like they've failed to catch up. But they are still totally legitimate muslims, and should be treated as such. No one goes to hell for being a Sunni. No one should be killed or hurt for being a Sunni. Sunni being the older sect, view the shia as deviation, apostasy. Contaminating the religion of the prophet. A shia is just a Kaffir, and in principle, must die. They will certainly go to hell. In light of the current battle, I remain hopeful that no human disaster should follow if shia militia liberate the Sunni populations. Crimes might and most probably will be committed, but not on the scale of policy or because of belief.

Now the second main difference is in Fighh, or how sharia law is extracted. Sunnah, means tradition. There are two sources for Islamic law in Sunni Islam: t book, and tradition(of the prophet and the first few caliphs) there is little room for interpretation here. Thus, some of the crimes by IS, like selling Christian women into slavery is really Islamic, as determined in both book and tradition. Same goes for many atrocities the Saudi do. Shia fighh, adds a third element to Book and Tradition, and that's 'reason'. Thus, if a shia top cleric, or 'mojtahid' declares modern slavery Haraam because it doesn't stand to reason, that's acceptable. And all who follow him, well, have to just follow him. In theory, this is supposed to keep the religion up to date. For example, it is not seen unislamic in Iran to send thieves to jail instead of cutting their hands, because the latter is no longer deemed 'reasonable'. Don't hold your breath though, the clerics who are allowed to use their reason! Are generally very old conservative men who generally prefer to keep things as they are. Yet there is some room for change and improvement. It is not difficult to spot the lesser of two evils. I think it should've come naturally to the West that shia populations would make more meaningful allies, I will never understand why they thought enriching and empowering Wahhabism, the most fundamentalist of Sunni sects, was such a brilliant idea.