There is no compulsion in Religion

لَا إِكْرَاهَ فِي الدِّينِ

“Let  there be no compulsion in religion”

(02:256)

The Quran clearly mentions the liberty and freedom of a person to choose his religion and is against forcing a person to accept Islam.

The religion of a person is related to one's soul, so forcing one to convert to a religion he or she does not believe in violate his soul, and so the result is nothing else than anger and hostility. In this respect, anyone who enforces one to observe religion of Islam acts mainly against the Quran. There is a great implication behind Islam's command of avoiding compulsion in religion. 

Islam has the literal meaning of "submission" and the Muslim is a person who has "submitted" himself. For a person to follow Allah's guidance with firm belief and to make an effort in His path, first of all that person should hold firmly to faith in Allah. Yet, if one becomes Muslim under duress, that person does not turn out to be a Muslim but a hypocrite. 

According to Islamic tradition, this verse was revealed by the Angel Jibraeel to Muhammad(SAW) during the Invasion of Banu Nadir. 

“World religions and norms of war”, a book published by the United Nations University, states that Quran 2:256: "there is no compulsion in religion" was mentioned about this event, the books quotes the Sunan Abu Dawud hadith^[1] below:

“When the children of a woman (in pre-Islamic days) did not survive, she took a vow on herself that if her child survives, she would convert it a Jew. When Banu an-Nadir were expelled (from Arabia), there were some children of the Ansar (Helpers) among them. They said: We shall not leave our children. So Allah the Exalted revealed; "Let there be no compulsion in religion. Truth stands out clear from error." 

Sunan Abu Dawood.

 Do you people remember how Islam was  strengthened by the conversion of 'Umar (May Allah be pleased with him) to the truth as brought about by the Prophet of God (Peace Be Upon Him). Was it by force?

'Umar (May Allah be pleased with him) was one of the nobles of the Quraysh, broad-shouldered, tall and brave. He was feared and respected by all. How the Prophet (Peace Be Upon Him) wished that he should accept Islam, as he often prayed to God for showing him the right path. Fatima bint al-Khattab (May Allah be pleased with her), the sister of 'Umar, accepted Islam and shortly thereafter, her husband Sa'id Ibn Zayd (May Allah be pleased with him), too, followed suit. But both kept it a closely guarded secret since they feared the violent inclination of 'Umar's nature. They knew that 'Umar was a zealous adherent of his forefathers' religion and carried a bitter aversion to the new faith in his bosom. Khabbab Ibn Aratt secretly taught the Qur'an to Fatima bint al-Khattab after her conversion. 'Umar planned to murder the Prophet (Peace Be Upon Him). One day he sallied forth, with a sword hanging from his neck to find out the house near as-Safa where the Prophet (Peace Be Upon Him) and his companions were reported to have assembled. Nu'aym Ibn 'Abdullah, who belonged to 'Umar's tribe of Bani 'Adiy and who had already acknowledged faith in the Prophet (Peace Be Upon Him), happened to see 'Umar along the way armed and fiercely agitated. He asked, "Umar, where are you going?" "I seek for Muhammad," was 'Umar's reply, "And I will slay him; he has forsaken our religion, shattered the unity of the Quraysh; ridiculed them and vilified their gods. Today I will settle the matter once and for all." "Anger has blinded you," retorted Nu'aym, "Would it not be better to set your own family in order?" 'Umar was taken aback. He asked, "And who are they in my family?" Nu'aym replied, "Your brother-in-law and cousin Sa-id Ibn Zayd and your sister Fatima. They have given faith to Muhammad (Peace Be Upon Him) and accepted his religion. Better deal with them first." 'Umar immediately hurried on to the house of his sister. Khabbab was at that time reading the Surah TaHa (20th Chapter of the Qur'an) to the couple from a manuscript he had with him. When they caught the footsteps of 'Umar, Khabbab hid himself inside a small room whereas Fatima instantly concealed the manuscript beneath her thigh. But as 'Umar had already heard Khabbab reciting the scripture, he demanded on entering the house, "What was this nonsense murmur that I heard?' "Nothing", both answered, but "What have you heard?" "Yes, I accidentally discovered," continued 'Umar angrily. "I know that both of you have joined the sect of Muhammad." With these words, 'Umar threw himself upon his brother-in-law. Fatima rushed in to save her husband, but 'Umar struck her hard and wounded her. All this happened abruptly, but now, both husband and wife boldly and openly asserted: "Yes, we are Muslims; we believed in Allah and His Prophet (Peace Be Upon Him); do whatever you will." 'Umar saw the blood flowing from the wound he had inflicted on his sister; his anger gave in to shame coupled with admiration for his sisters courage. Cooled down, he asked for the manuscript that he had heard Khabbab reading. He said "Show me the manuscript. I want to know what Muhammad has brought." In reality, 'Umar knew the art of reading and writing. Fatima, however, replied, "I fear what you might do with it." "Umar promised, with solemn assurance, not to destroy it. Fatima, too, thought that he might change his views after reading the scripture. She said to him politely but firmly, "My brother, you are unclean because of your polytheism, and only the pure can touch it." 'Umar rose and took a bath. His sister then gave him the pages on which Surah Ta Ha was written. “Indeed, I am Allah . There is no deity except Me, so worship Me and establish prayer for My remembrance.”  He had read only a few lines when he exclaimed in amazement, "How noble and sublime is this speech!" Thereupon Khabbab came out of his concealment and said, "O 'Umar, by God, I hope that Allah would bless you with His Prophet's (Peace Be Upon Him) call; for I heard him just last night imploring earnestly; "O Allah, strengthen Islam by Abul Hakam (Abu Jahl) or 'Umar Ibn al-Khattab.”  Now, 'Umar have some fear of God." 'Umar (May Allah be pleased with him) asked Khabbab to lead him to the Prophet (Peace Be Upon Him) so that he might accept Islam. On being told by Khabbab that the Prophet (Peace Be Upon Him) was in a house at as-Safa with his companions, 'Umar (May Allah be pleased with him) immediately took his sword and headed for him. When 'Umar (May Allah be pleased with him) knocked at the door indicated by Khabbab(May Allah be pleased with him), one of the companions got up through a chink in the door to be sure of the person. Seeing 'Umar (May Allah be pleased with him) with his sword on, he hurried back appalled to report, "Prophet (Peace Be Upon Him) of Allah, 'Umar Ibn al-Khattab is here armed with his sword." Hamza (May Allah be pleased with him) intervened to say, "Let him in. If he comes with a peaceful intent, then it is alright, but if not, therewith we will kill him with his own sword." The Prophet (Peace Be Upon Him) ordered the companion to open the door for 'Umar to enter and thus join them. As 'Umar (May Allah be pleased with him) entered the door, the Prophet (Peace Be Upon Him) went forth to meet him in the room. He seized his cloak and pulling it rather firmly, said to him, "What for have you come, O son of Khattab? By God, I see that some calamity is to befall you before you have the final summons." But 'Umar (May Allah be pleased with him) replied submissively, "O Messenger of Allah, I have come to attest my faith in Allah and His Prophet (Peace Be Upon Him) and what he has brought from God." The Prophet (Peace Be Upon Him) raised the cry of Allah-O-Akbar so loudly that all the companions present in the house came to know that 'Umar (May Allah be pleased with him), had just accepted Islam.  (Ibn Hisham, Vol. I, pp. 342-46).  'Umar's (May Allah be pleased with him) conversion was a turning point in the fortunes of Islam as it made Muslims feel all the more confident and strengthened. Hamza (May Allah be pleased with him) had already accepted Islam beforehand, and now with 'Umar's (May Allah be pleased with him) conversion, the Muslims knew that it was likely to send the Quraysh in jitters. They were particularly embittered on learning of 'Umar's (May Allah be pleased with him) conversion. The Muslims were thus right in their reckoning for none of those who had embraced Islam in the past made such a stir nor created such a tense excitement and impact as did that of 'Umar's.  So I invite the Muslims and Non-Muslims as well to read the Quran and ponder on its meanings. Especially Non-Muslims, just read it once with translation and you'll come to know about its miracles, about the things told 1400 years ago that are recently being discovered by modern science.   The Glorious Qur’an is the constitution revealed by God (Allah) to regulate and govern human life. It speaks with the perfect knowledge of the Creator about His creation. It exposes the truth and invites mankind to the way of truth. It is the Book about which, there is no doubt. “This is the Book about which there is no doubt” ( 2: 02)