If you want to know either the history of Islam in general, and especially if you want to know about Islamic theology, Islamic Imperialism is not the book you want. It's what its title describes--a history of empires and imperialist ideologies under the banner of Islam--and discussion of theology other Islam-related subjects is incidental and given only to support the thesis. You largely can't learn from this book what Muslims believe.
That said, it fully explains how for Muslims (especially Arab Muslims), dreams of regional and even world domination are inseparably tied to Islamic beliefs. The key is that unlike Christianity, Islam makes no distinction between sacred and secular government, and so notwithstanding that there is currently no Islamic caliphate (it ended with the defeat of the Ottoman Empire in World War I), Muslims believe that Islam must politically govern the entire temporal world.
Although quite short (under 250 pages) and concise in style, this book is written in a very academic (if concise) style. It expects the reader to already know basic details of Islamic political history (such as the difference between a "caliph" and a "sultan"), and it occasionally uses obscure terms without bothering to explain them.