The invasion of Islam
While Heraclius was on his way to the Persians, a new religious movement was born on the Arabian Peninsula, which its initiator successfully spread – prorok mahomet. Soon the Arabs became a powerful political force that threatened the monarchies of that time, especially the Persians and Byzantines, weakened by the wars. Already in 635 r. Muslims united under the slogans of "holy war" captured Damascus, then they entered Asia Minor and besieged Constantinople for several years without success (674). They faced the famous "Greek fire", that is, the substance fired from the pipes, which ignited spontaneously upon contact with the target. The work of Heraclius was lost due to the Arab invasion, the empire lost not only Syria and Palestine, but also Egypt with all of North Africa. These countries were the most developed provinces of the state, so their loss was a severe blow to the empire. The symbol of this difficult situation was fact, that after the loss of Egypt, which was, in a way, a granary of the Byzantine Empire (main supplier of wheat), the free distribution of bread to the people in Constantinople ceased, which was a tradition inherited from the Roman Empire.
After the unsuccessful siege of Constantinople, the Arabs made a thirty-year peace with the empire (678), but his problems did not end there. From the north, the Bulgarians began to push, with whom Emperor Constantine IV had to sign a treaty formally establishing the Bulgarian state in the lands previously belonging to Byzantium. This clearly showed the weakening of the empire, which translated into the next several dozen years. A new peace treaty was concluded with the Arabs, but already in 691 r. the war for Armenia was lost with them. Fights for the throne broke out in Constantinople, coups d'état, thus frequent changes of the ruler were the order of the day. The situation changed after the vigorous Leon ascended to the throne 111 (717 – 741). In year, in which he sat on the throne, Muslims wanted to conquer Constantinople again, but after a year of siege, they gave up on this plan, which strengthened the position of the emperor.