User blog comment:Vivienne North/The Rest of the World/@comment-1153722-20120630072714

For a simple answer, take a look here. For a less simple answer, read on.

The history of the Assassins is rich and complicated. The earliest known Assassins were located in the Persian Empire, and later the Macedonian Empire. They were also active in China by the time the Qin Empire was founded, and later in the Roman Empire and northern Africa (Egypt).

By the time of the Middle Ages, the Assassins were no longer located in Europe but operated mostly in Asia, namely the Crusader States of the Levant and the Mongol Empire. During Altaïr's time as Mentor, he began spreading the ideologies of the Order again to several places around the Levant, but it was only when Niccolò and Maffeo Polo resided some time in Masyaf when the Assassins began being more widespread. After the Polos left Masyaf, Altaïr disbanded the Assassins from Masyaf and sent them around the world, and the Polos founded guilds in Constantinople in the Ottoman Empire and in Venice. Altaïr's grandchildren left for Alexandria and Egypt, and one of his descendants became a Mentor of the Egyptian Assassins.

By the time of the Renaissance, the Assassins were mainly focused in Italy, where the leadership of the Templar Order was also located. The Assassins and Templars were spread throughout most of Europe, northern Africa and Asia, namely England, the Holy Roman Empire (the Netherlands, Germany, Austria, Switzerland), Italy, Greece, the Ottoman Empire, Tunisia, Libya, Algeria, China and India. Around 1503, the Assassins and Templars spread to the New World, to what would later become North and South America.

By modern times, the Assassins were spread around the globe, having numerous safehouses, camps and hideouts in cities, towns and remote locations. It was also during the 20th century that all branches of the Order were united under one single Mentor, while before each branch had its own Mentor or ordinary leader. The Great Purge in 2000 and its aftermath during the following years eradicated most Assassins, and the Assassins were forced to become even more secretive, only operating in small teams of (usually) four Assassins. Even those teams were eradicated at a fast pace, and by 2012 there was only five known Assassin teams (including Desmond's team) and a headquarters somewhere in Europe.