The outbreak of religious war in Iraq should not lead to UK or US military intervention. Many people living in the west are unaware of the issues in dispute between Sunni and Shia Muslims, and are not on either side. We are not well briefed over the theological. social and political differences, which clearly mean a lot to those involved.
When Western Europe lived through its own religious wars, with Catholic fighting Protestant, issues of national identity and borders came up in the conflicts, just as the religious wars in the modern Middle East also pose these secular issues and power struggles. The revolt of the Netherlands against Spanish rule was both a religious battle, and a quest for national identity and self government. It was good that Islamic armies and navies stayed at home and did not come to Western Europe to help one side or the other or impose their view of the right answer on the warring factions. If they had tried to intervene there might have been more deaths and a more complex struggle.
In today’s complicated world the great western powers do have duties as members of the UN. Where the international community thinks international law has been breached by one side in the dispute and not the other, and where they think their military intervention could put right the wrong, then there is a case for doing so. The liberation of Kuwait is a good recent case. Most in the Arab world thought the liberation of Kuwait was a just cause. Kuwait herself wanted military assistance. The west was able to do it quickly and successfully.
The internal wars in modern Syria and Iraq, part religious, part power struggles, do not pose the same straightforward moral issues. Nor is their the same opportunity for western military might to enforce a new and better solution at an acceptable cost in human life and destruction of property. The government of Iraq can ask for military help, and it may be that technical advice or supplies of equipment are possible and permissible. Going further would be unwise. The West has taken sides, backing the government in Iraq but against the government in Syria. It has wisely fallen short of backing the opposition in Syria, given the varied nature of that opposition and the difficulty of knowing how stable government could emerge from the violent overthrow of an unpleasant regime. Sometimes the west has to accept there should be limits to its interventions.