The worst tyrants of those days were the rulers of Persia and Rome...
The worst tyrants of those days were the rulers of Persia and Rome, the greatest two states with the mightiest armies in the world. The Romans, only few years before then, had achieved victory over the Persians, hence they considered themselves more powerful and more mighty. Suddenly, they had now to face a challenging force: that of Islam. The arrogant usually fear the revolutionary movements, specially the ideological ones; hence, the Romans decided to end the newly born Muslim force.
The Muslims got the news of the mighty Roman army of 40,000 fighters heading towards their borders. Some of the Arab tribes of the distant borders joined forces with them. The Muslims received such news while they were suffering from a shortage in food and had not yet harvested their crops. However, the worshippers of Allah, the true believers, knew that the defense of Islam had a priority over all other matters. The Prophet (P.B.U.H.) ordered them to prepare themselves to fight the Romans.
Few days later, some 30,000 Muslims made their approach towards the war front. Some could not find the necessary weapons and, hence, could not join the Prophet in this expedition of TABUK. The Prophet (P.B.U.H.) left Ali (as) behind in the city to protect it against sudden plots of the hypocrites. He (P.B.U.H.) said to him, "You are to me as HAROUN (Aaron) was to MUSA (Moses), only no Prophet shall come after me".
Suffering the hardship of the journey, the Muslims' army reached TABUK to find out that none of the Roman soldiers were there: they were scared to death and withdrew inside the country in order to avoid being defeated by the Muslim army. The Muslim spent a few days in TABUK where the Prophet (P.B.U.H.) signed friendly treaties with some of the dwellers of that area.
Then the Muslim army made its way back to AL-MEDINA where news of their victory was ahead of them, and people gathered to welcome them back. The news of the fleeing Romans spread at large and the Arab tribes felt no more fear of the arrogant enemies. The Muslim army became a major force in support of all oppressed people.
The suffering cries of AMMAR son of YASSIR, under torture, the moaning of BILAL the ABYSSINIAN on the burning sands of the desert outside Mecca, the shedding of HAMZA'S blood (the Prophet's uncle) and the blood of other hundreds of martyrs did not go in vain. All became a fruitful tree for humanity. They enjoyed the rewards of safety and were freed from slavery.