Were non-Muslims initially required to convert to Islam?

Answer 1

The message of Islam was, and still is for all non-believers. There is no compulsion in accepting Islam. Non-believers may or may not not convert t Islam. Islam does not force anybody to change his beliefs.

Answer 2

Generally, No. There is an important "but" though as well as lapses in this tolerant policy.

While Islam has not usually used forcible conversion, it is not correct to say that it never occurred and two major such instances are detailed below. Also, many polytheists were forced to abandon their faiths at the point of a sword. Additionally, in almost all Islamic contexts, there was strong societal pressure to convert to Islam event if there was no sword pressed to a person's neck. Finally, conversion out of Islam was criminal in all Islamic States prior to 1800 and would receive the death penalty in numerous cases. This meant that anyone "born as a Muslim" was compelled to practice Islam regardless of whatever that child would have wanted to believe, even if his grandparents or even his mother was non-Muslim.

Discriminatory Treatment of Non-Muslims to Encourage Conversion
The Dhimmi, or non-Muslim under Muslim occupation was required to pay a number of taxes that were connected with his Dhimmi status. The most famous was the jizya, which was a tax that Dhimmi had to pay for Muslims for the right to not be killed where they stood for not acknowledging Mohammed's Prophecy; it was a form of humiliation. Additional taxes included the kharaj, which was a tax on non-Muslim land-holdings in the Muslim World. The kharaj was so untenable that most Dhimmi were forced to live in the cities where the tax would not be applicable. Justice was also a problem. On paper, a Christian or Jew could testify against a Muslim, but in reality, such testimony was not acceptable and the attempt to defame a Muslim would receive retribution. Christians and Jews were not allowed to build new houses of worship, restore old houses of worship, proselytize in any way (this included religious debate or dialogue), or allow wine or pigs to be shown in public.

The Forcible Conversions of King Aurangzeb
Depending on the Muslim ruler of India, there were events of forcible conversion. King Aurangzeb is well-known in India for this act as well as destroying major Hindu Temples such as the Kashi Vishwanath temple, Kesava Deo temple and Somnath temple. He was vicious to both Hindus and Sikhs and severely limited the privileges given to Christians by the preceding kings. However, his grandfather, Akbar the Great was known for permitting the free and equal practice of religion.

The Ottoman Process of Devshirme
The process of Devshirme robbed innocent Christian citizens of their children in the Balkans. The parents would have no choice as to whether their children would be deprived from them. It was a tax. They would be brought to the Sultan in Istanbul and forcibly converted to Islam at the tender age of five years. The women would grow up to be part of the Sultan's harem. While they served the Sultan, each woman could hope that her son would be chosen as the Crown Prince and she could have court rights, but she could never hope to have rights to her own body. The men were educated in the arts of war and diplomacy. The ones of who were more physically capable would become the feared shock-troops of the Ottoman Empire: the Janissaries. Those more skilled in diplomacy would be the ministers of the Sultan's court.