D.K. Fieldhouse's "Western Imperialism in the Middle East"

The two volumes by Yapp on the making of the modern near east before and after the first world war.

The early chapters of Tripp's History of Iraq.

I haven't finished it yet but Ali Allawi's new biography of Faisal looks excellent.

Peter Sluglett's "Britain in Iraq: Contriving King and Country." (have to admit having only skimmed it but it seems good, well cited.)

Eugene Rogan's The Arabs, A History.

All of those mark a good starting place and cover British middle east policy in good detail, well sourced, and from multiple perspectives.

That daily beast article, on the other hand, is a bit of a mess. I would disagree with many of its conclusions and summations. For one thing it totally ignores why Bell wanted to do any of this, namely that there was an enormous rebellion against British occupation in 1920 and she thought Iraqi self-rule was better for all parties.

It implies a conscious divide and rule strategy as you say but then says that "In reality, the Iraqi borders had been arbitrarily drawn and disregarded 2,000 years of tribal, sectarian, and nomadic occupation." Iraq could have been formed in a way to divide and rule or it could have been formed arbitrarily. It cannot have been both.

In fact it was less divide and rule than sort of a three legged stool that was designed to unite into one country led by Faisal. To call it arbitrary is to ignore what happened. Misguided, probably. The alternatives were not much better.