Were the majority of the Islamic conquests carried out by the Ash‘aris?
Question

I heard someone say that all those who achieved conquests were Ash‘aris, such as Salaah ad-Din al-Ayyubi, Muhammad al-Faatih, ‘Umar al-Mukhtar, and others, and there was no one who was Salafi. Is this true?
Praise be to Allah.Most of the conquests happened at the time of the earliest and best generations, such as the conquests of the Persians and the Byzantines, and the conquests of Syria, Egypt, North Africa, Andalusia, India and Sindh; in other words, from the ocean to the ocean. All of that happened before Abu’l-Hasan al-Ash‘ari was even born!
But after the era of al-Ash‘ari (d. 324 AH), whatever wars or conquests took place, people of mixed backgrounds took part in them, and whether the commander was a Salafi or an Ash‘ari or a Karrami, all kinds of people took part in them. For example, Ibn Qudamah and other people of Bayt al-Maqdis, who were Salafis, took part in campaigns with Salah ad-Din, and Ibn Taymiyah took part in the wars against the Tatars.
This argument is pointless and that there is no evidence in it to suggest that a certain school of thought (in ‘aqidah) is right or wrong. If conquest was proof of the soundness of a belief, then all of the early conquests would point to the soundness of the Salafi madhhab.
But what we may learn from this discussion is that when the ummah is faced with external danger, they unite, cooperate and set aside their differences, and the Salafis fight alongside the Ash‘aris and the Sufis to repel the enemy who, if they conquer the Muslim lands, will commit mischief without differentiating between one school of thought and another.
As for the one who has some innovated beliefs or practices, he may be excused if he based his innovation on his own efforts to reach a conclusion, or it was based on the misinterpretation of some text, or he followed a shaykh in that regard. So he is not to be punished for his innovation, and he may be rewarded for his good intention and efforts to reach the right conclusion, as well as his efforts in support of Islam. This is how Ahl as-Sunnah evaluate many of the scholars who were known for their knowledge, righteousness and jihad, if they belonged to a group that followed innovation. They seek excuses for them and think positively of them; they mention the virtues that they had and they note that they did not refrain from striving in jihad, whether the ruler was righteous or evil.
Al-Hafiz Ibn Kathir said, in his biography of the righteous shaykh Abu ‘Umar al-Maqdisi:
… He was the brother of Shaykh Muwaffaq ad-Din ‘Abdullah ibn Ahmad ibn Muhammad ibn Qudaamah. Abu ‘Umar was older than him, because he was born in 528 AH, in the village of as-Sawiya – or, it was said, in Jama‘il – and he raised Shaykh Muwaffaq ad-Din; he treated him kindly, helped him to get married and took care of him.…
He and his brother, and his maternal cousin al-Hafiz ‘Abd al-Ghani and his brother Shaykh al-‘Imad never stayed behind from any campaign in which the ruler Salah ad-Din went out to the land of the Franks. They were present with him at the conquest of al-Quds (Jerusalem) and on other campaigns."(Al-Bidayah wa’n-Nihayah  17/21).
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
Not everyone who differs in some matters of creed is necessarily doomed. The one who differs (regarding some matters of creed) may have studied the religious texts but come to a wrong conclusion, and Allah may forgive his mistake. Or some text concerning that issue may not have reached him, on the basis of which proof could be established against him; or he may have some good deeds to his credit by means of which Allah will erase his bad deeds. If there is some word of warning in the religious texts that applies to him, of the type for which the one who misinterprets the text or repented, or the one who has good deeds that could erase his bad deeds is not included in the warning, then it is more appropriate [to believe that such people will not be doomed]."(Majmu‘ al-Fatawa (3/179). See also: Mihnah Ibn Taymiyah in ash-Shaamilah (34).
Whatever the case, what matters is following the Qur’an and Sunnah, and the way of the Companions of the Prophet (blessings and peace of Allah be upon him), for this is the criterion by which we may determine whether a belief is sound or not. As for jihad, it is something that a Khariji or Mu‘tazili or Sufi or Ash‘ari or Sunni may be involved in, and it is not indicative of the soundness of his belief.
In the modern era, the Salafis have fought in jihad, conquered lands and attained victory, and they are no less in that regard than others.
And Allah knows best.