Quran 61:9 – “It is He who sent His Messenger with guidance and the religion of truth to manifest it over all religion, although those who associate others with Allah dislike it.”

Islam will prevail over all religions because it is the Truth. People will embrace Islam even when there are mischief-makers who want to spread lies in order to keep people away from the Truth (Islam). The verse (Quran 61:9) says nothing about fighting, or forced conversion.

Commentary

Tafsir Ibn Kathir

(They intend to put out the Light of Allah with their mouths.) indicating that the disbelievers will try to contradict the truth with falsehood. Their attempts are similar to one’s attempt to extinguish the sun with his mouth, which is impossible. Likewise is the case of their attempt to extinguish truth.

So Allah said, (But Allah will bring His Light to perfection even though the disbelievers hate (it). He it is Who has sent His Messenger with guidance and the religion of truth to make it victorious over all (other) religions even though the idolators hate (it). [1]

Muhammad Asad

10 Cf. 3:19 – ‘the only [true] religion in the sight of God is [Man’s] self-surrender unto him’. [2]

Malik Ghulam Farid

3040. Most commentators of the Qur’an are agreed that this verse applies to the Promised Messiah, because in his time all religions will have made their appearance and the superiority of Islam over all of them will become established. [3]

Tafsir al-Jalalayn

It is He Who has sent His Messenger with the guidance and the religion of truth, that He may make it prevail, that He may raise it, over all [other] religions, [over] all the religions which oppose it, though the disbelievers be averse, to this. [4]

Maulana Muhammad Ali

9a. Verses 8 and 9 contain two different prophecies. In the first of these we are told that all attempts to annihilate Islam will fail, and they did fail. In the second it is affirmed that Islam will be made the predominant religion, the truth of which was witnessed by Arabia in the lifetime of the Holy Prophet. But both prophecies have a wider significance.

Attempts shall be brought to naught; while the predominance of Islam over all the religions of the world would in time be established, as clearly as it was in Arabia. The commentators say that this predominance will be brought about through the Promised Messiah (Rz). Polytheists, it should be noted, include the Christians, for they adopted the polytheistic doctrine of Trinity. [5]

References:

[1] Tafsir Ibn Kathir http://www.qtafsir.com/index.php?option=com_content&task=view&id=1367&Itemid=117
[2] The Message of The Quran translated and explained by Muhammad Asad page 1170
[3] The Holy Qur’an Arabic Text With English Translation & Short Commentary by Malik Ghulam Farid page 1133
[4] Tafsir al-Jalalayn – http://www.altafsir.com/Tafasir.asp?tMadhNo=0&tTafsirNo=74&tSoraNo=61&tAyahNo=9&tDisplay=yes&UserProfile=0&LanguageId=2
[5] The Holy Quran Arabic Text with English Translation, Commentary and comprehensive Introduction [Year 2002 Edition] by Maulana Muhammad Ali Page 1089