the majority in Iran, Iraq and Bahrain. The Bahrain ruling family is Sunni however and the whole thing can be complicated in Bahrain. Lebanon is not a majority Shia or Sunni population as Lebanon has a real mix of religions. The Palestinians are overwhelmingly Sunni. The countries we sometimes call the "Gulf States" were heavily manipulated militarily in battles and coup attempts by the US, UK and France after WW2 with the majority of screwing around being the US and UK and sometimes enlisting the help of Israel. They are majority Sunni except for Oman which has a separate offshoot of Islamic religion. Turkey is majority Sunni. Kuwait is Sunni.
Nasser in Egypt was extending his power and influence throughout the Middle East specifically in efforts to kick the UK colonialists out. The US and UK wanted to protect their oil and shipping interests and they proceeded to prop up, then undercut and pit the various factions in all the different countries against each other in a carousel of follies throughout the late '40's and into the '70's. Our media of course ignores all of this history of our f*cking around and f*cking over all of the various factions. Especially when they discuss Yemen for example.
We always have to keep in mind the Sunni and Shia thing because while it is not like they are cutting each other up the religious differences in countries deep into their religion are always important if not always openly made a point of conflicting views.
Hamas is majority Sunni and Hezbollah is majority Shia. An easy way to conceptualize it is that the "Northeastern" countries in the Middle East are mostly Shia.