Fidem Pacis

The premise of this althist is based upon the legend that in the year 628 AD the Prophet Muhammad sent envoys to the emperors of Rome and Persia, inviting them to convert to Islam. In the OTL, even if the legend is true the envoys were ignored. In this timeline, the Roman Emperor, Heraclius, was curious enough to personally investigate the new religion, ultimately leading to his own conversion and to the Arab conquest of the Middle East being averted.

I'll be uploading a full timeline later, but for now here are some of the key differences from the OTL.

Comparisons with the OTL

 * Heraclius and eventually the rest of the Roman Empire, converted to Islam, making them allies of the Arabs. Roman authority was able to rein in Arab religious fervour, preventing their conquest of half the world. Islam spread anyway just as rapidly, but it was by peaceful means and there was not much religious tension in the centuries to come.
 * The Roman Empire, despite passing through several periods of weakness, survives to this day in Greece and Anatolia. Until relatively recently it even continued to hold Egypt and Syria. Italy, North Africa and the Balkans are all fully Romanised, even though they haven't been ruled by the empire for centuries.
 * The Visigothic Kingdom in Spain remained strong and survives to this day, though culturally it's pretty similar to OTL Spain. Portugal is not independent, but its place as a great power during the Renaissance is largely taken by Aquitaine, which remains strong.
 * The Welsh were able to resist the expansion of the Anglo-Saxons, and eventually pushed them out of most of southern Britain. As such the politics of Britain are effectively reversed - the most powerful and numerous people are the Welsh, with England roughly occupying the territory of OTL Scotland, and East Anglia being populated by the remnants of Frisian settlers.
 * Ship-building technology progressed faster, and the Norse discovery of Vinland was never forgotten. When the Greenland colonies had to be abandoned as in OTL, the survivors were able to resettle in the New World. As such, the main original colonial powers are Norway, Wales, France and Aquitaine, with Spain not even getting a look in.
 * Persian civilization remained strong, and was able to survive intact invasions by Turks and Mongols, as well as Romans and Arabs. However, united by an opponent they could never fully conquer, the Mongol Empire never fully disintegrated. The Chagatai Khanate remained strong, and over several centuries subdued once more the nomadic tribes of the steppes. This meant that Russia was never able to expand east, and it was eventually incorporated into Poland-Lithuania.
 * China established official diplomatic relations with Rome quite early on, and learned about the New World at the same time as Rome did. The voyages of Zheng He were directed east, not west, and China developed trading relationships with the natives of OTL California and the Oregon country. Later Chinese colonies were established here as well, so that European expansion across the continent was never quite able to reach the Pacific.
 * By obtaining gunpowder weapons from China, the Aztec Empire avoids being conquered by Europeans. The Aztecs survive as an independent power, and by the present day control much of OTL Mexico.

Aims

 * I have a rough outline of the timeline to the present day, though at the moment only the first 50 years or so after POD are done in detail. Bit by bit I'm slowly improving the rest.
 * I can't pretend to know a lot about non-European history, so what I have is pretty Euro-centric. Eventually I want to explore in more detail how some of the Asian and African nations are affected.