In their book "ISIS: Inside the Army of Terror" from early 2016, Michael Weiss and Hassan Hassan give detailed insight into the Islamic State, its origin, key members, alliances, critical battles, and strategy of terror. The story begins with the early ties between Ayman Mohammed Rabie al-Zawahiri and Osama bin Laden in the 1990s, and the later split between them and the more radical and extreme Abu Musab al-Zarqawi. Their disagreement on who are their enemies, crucially whether it includes Muslims or not, has underlined the split between al-Qaeda and ISIS / Islamic State. In later chapters, the rise of the current leader, theology professor Abu Bakr al-Baghdad, is investigated. The book goes into great detail about several key battles in Iraq and Syria, and analyses positions and outcome. Finally, some of the terror attacks on civilians in Europe and the US is put in context.
Sunni vs. Shia
There are a few important take-aways from the book: The divide between Sunni and Shia Muslims is usually at the core of most of the conflicts. Crucially, the numbers goes a long way to explain the various positions: Word-wide, Sunnis are in majority at around 85–90% while 10–15% are Shia. However, in Iraq and Iran this is reversed, where 80% and 95% are Shia respectively. An important point is the fact that Saddam Hussein was Sunni, and his mostly Sunni minority Baath party ruled over the Shia majority. When US invaded and ended their rule and tried to create democracy, the stage was set for bitter conflict. Furthermore, Paul Bremer (presidential envoy to Iraq) fired the mostly Sunni Iraqi army, along with most other official positions. So around 2003 a large part of the previous Iraq elite was suddenly jobless, but with plenty of military experience and even weapons on their hands. al-Zarqawi exploited these fault lines to his fullest, and ignited the ensuing civil war.
A similar setup, but again reversed has been the background for the civil war in Syria. There, Bashar Hafez al-Assad and his party are Alawites, a branch of Shia, but in a minority at around 13%. When the spring revolutions in 2011 swept other Muslim countries, al-Assad pitted themselves as under attack by the Sunni (74%) majority. al-Assad's regime has support from Iran and Hezbollah who are also Shia. The opposition in Syria has many factions, and ISIS has time and again proved that they are experts at driving a wedge between opposing forces to divide and conquer.
Enemy of my Enemy
From small tribes, to national organizations and rebel groups and all the way to international alliances, the relationships network is extremely complex. A graph like this hardly scratches the surface. Furthermore, alliances shift frequently, and often the short term strategy is "the enemy of mine enemy is my friend". This can be seen going far back, and characterizes much of US and Russian involvement in the various conflicts: During the Cold War; the US backing of Iraq against Iran in 1979; later US attacks against Iraq; US backing of the Kurds. Iran and Russia have tended to back the opposite groups, and Iran in particular has now infiltrated much of the Shia resistance and politics in Iraq.
The book goes into detail on several of these fluid alliances, and looks at the decisive battles and opposing personalities. The point is made many times over that in order to understand the conflicts, one has to understand the tribal politics. At a higher level, the relationships are often more pragmatic: Although ISIS is waging war across Syria, and also against al-Assad forces, they have a business relationship in the oil trade, where ISIS is selling back oil to al-Assad's regime from the oilfields they have captured. al-Assad benefits since ISIS also fights the rebels in Syria. The enemy of mine enemy is my friend.
Weiss and Hassan have done plenty of research and interviews for this book, and it shows through all the details revealed. They have also done a good job of explaining the background history, religious underpinnings, and political motivations for the parties involved in the conflict. However, it can get somewhat tedious to go through all the nitty-gritty, and the writing style can be trite with the occasional odd analogies.
Overall, the book is definitively worth a read if you are interested in the current conflict, want to understand the terror attacks. Regional and international politics become more clear with the information provided by this book.