Well, Muslim opposition and strife with other Muslims is more relevant than with other Muslims in many cases, because every Muslim ethnic group, faction, or nation wants to promote its interest in the respective region.
in Iraq today Shia and Sunni factions are fighting each other more intensely since the 2003 invasion of Iraq, bombings in the capital with as up to hundreds of casualties have become common news. the Kurds are also at odds with the Sunnis in northern Iraq. modern middle eastern history is scarred with numerous conflicts between nations and factions, its hard to even begin listing it. there are millions of casualties and millions of refugees in Islamic lands in the Middle east and in Africa only in the last 30 years.
around my nation, in the north Lebanon has known several civil wars between different factions, Syria has been competing with nations such as Jordan on regional dominance with threats of war in the past, during the 70's the Jordanian government led the death of up to tens of thousands of Palestinians in the Black September conflict.
practically every nation in the region has warred with neighboring Arab or Muslim nations or had troublesome fighting within its own borders.
This is a long struggle for power and interests, that will go on through out all Islamic history. sometimes because of religious zeal and intense disagreement in dogma, in the case of certain militant groups, and other times because of power projection and the need to stay on top in a dog eat dog region.
right now, one of the main issues in the middle east, is various Sunni Arab nations concern with the rise of the Shia bloc led by Iran, the leader of Jordan King Abdullah II and the Egyptian president, Hosni Mubarak in recent years have propagated much concern in the Arab world over the rise of Shiite Iran, the gulf states are voicing the same concern and attitude, with some gulf states strategists going as far as promoting an Israeli strike on Iranian nuclear facilities, in 2009 Morocco cut ties with Iran over what the Moroccan leadership claimed was Iranian intervention in the religious fabric of the Moroccan kingdom. the Sunnis in the region are worried about the expansion of the Shiite bloc in their lands, and the influence of a regional power in the case of Iran over Shiites populations in the region. Iran has been linked to Shiite militias in Iraq, and has also been hinted in intervention with the Shiite militias in Yemen who have been warring with the official government, the Iranian influence over Shiite Lebanon and Hezballah the militant Shiite organization in Lebanon is well known, as well as its influence and support of (Sunni) Hamas in the Gaza strip.