Stemmed from a number of causes, including: unpopular legislation from London (e.g. the Stamp Act and the Quebec Act); a rise in American national consciousness thanks to efforts to instil one to raise troops for the Seven Years' War, and other factors (Ben Franklin being involved); a new royal regime which was unpopular both at home and in the colonies, but the latter felt their interests were not being represented in the attempts to circumvent it; increasing tax; and the fact that now that the French had been kicked out of North America after the Seven Years' War, there was no longer a big scary threat to justify to American colonists that they needed to pay for the British army to defend them.
Lasted from 1775 to 1783, though the first couple of years were mostly scattered skirmishes and the last couple saw little action in America itself.
Often neglected is the fact that the ARW was a world war, like the Seven Years' War before it: France, Spain and the Netherlands entered the war on the side of the American rebels. The worldwide aspect of the war is sometimes called the War of the Bourbon Alliance. It also changed popular perceptions of the war in Britain. Before the U.S.-Bourbon alliance, a large part of British liberal and intellectual society saw the American colonists as fighting for a just cause, having been unfairly treated, and many high-profile soldiers and sailors refused to fight them. This, together with funding cuts to the armed forces, resulted in the British Government hiring German mercenaries who then behaved badly in the Americans, driving more colonials over to the pro-independence side. After the Bourbon alliance, however, many former American sympathisers in Britain saw them as having betrayed their stated goals of liberty and freedom by allying with tyrannical regimes, and only a few remained thereafter. (Some of the latter, like Joseph Priestley, emigrated to the fledgling USA to escape persecution at home for such sympathies).
After the pro-independence side, the 'Patriots', won the war, some of the remaining Loyalists fled to Canada or Britain, often after their lands had been confiscated.
Several ARW battles are well known, including early ones restricted to American rebels vs Britain, such as Saratoga and Bunker Hill; however, the most decisive was the Siege of Yorktown in 1781, where the Americans were strongly supported by the French and Spanish. This resulted in General Cornwallis' surrender, the British band played 'The World Turned Upside Down', and the war was effectively lost in America, though it dragged on elsewhere for another couple of years.
Probably the most common what-if is “What if the American Revolution had been avoided?” by, for example, less intransigent British governments or a central system of power in the colonies to engage directly with London.
Then there's “What if the colonies lose the war?” which may or may not be different - some authors have the ARW forgotten as a minor rebellion and footnote of history, while others still have pro-independence terrorist groups active in the modern successor to the colonies and that sort of thing.
A final strand is that of Ameriwank; even though the war ended rather well for the Americans, there are some who will try to get Florida for the USA or have the expedition to capture Quebec succeed (probably the least unlikely of these suggestions) or have the fledgling Continental Navy do better, and so on.