Prophet Muhammad and his Companions conquered Makkah peacefully. This was the home of the Prophet (p) and its companions who were persecuted and pursued even when they left to find safe sanctuary in Madinah.
The conquest of Makkah took place as a consequence of the Quraysh, they instigated the banu Bakr in fighting against Khuza’a, as a result many men of the Khuza’ah were killed. As a result of the Quraysh’s involvement and the killing of the Banu Khuza’ah’s people, the conquest of Makkah took place.
What made this conquest special was that all the Makkans who were hostile and had been involved in persecuting Muslims were all forgiven. Except for few individuals who murdered innocent people, they were dealt with or forgiven.
It is claimed by some that when Makkah was conquered the Prophet (p) thought about fighting other tribes and make them accept the faith of Islam by the sword. However, this claim has no historical truth to it. It was not the Prophet (p) who started hostilities against the Hawazin and Thaqif, they were the ones who mobilised other tribes to go to war against the Muslims.
The whole reason for the battle of Hunayn took place was as a consequence of the the Hawazin and Thaqif tribes were hostile against the Muslims and their hatred got in the way of them and made preparations to attack the Muslims in Makkah. The Prophet (P) having received news of them preparing to attack the Muslim community, he told his companions to prepare to engage the enemy.
Kitab Tabaqat Al-Kabir – Ibn Sa’d:
“THE GHAZWAH OF THE APOSTLE OF ALLAH AGAINST HUNAYN, AND THE SAME WAS THE GHAZWAH OF HAWAZIN
… They (narrators) said: When the Apostle of Allah conquered Makkah, the notables of the Hawazin and the Thaqif moved from one side to the other. They assembled and rose in rebellion.
Malik Ibn Awf al-Nasri had brought them together and he was then thirty years old. He ordered them and they brought with them their wealth, their women folk and their children. They mobilized at Awtas and the supporters were coming to them. They agreed on marching against the Apostle of Allah.” 
“The Prophet had been staying in Mecca during the year of its conquest for only a forth-night when [he received the news that the clans of [Hawazin and Thaqif [were marching against Mecca and] had already encamped at Hunayn intending to fight him.
Hunayn is a valley next to Dhu al-Majaz. Both the aforementioned tribes had assembled before [their match] after hearing about the Messenger of God’s departure from Medina, thinking that he was intending [to invade] them.
When he learned that he had occupied Mecca, Hawazin marched against him [to Mecca] with their women, children, and possessions. Their leader was Mailk b. Awf from the Banu Nasr.
[The clans of] thaqif joined forces with them and encamped at Hunayn intending to fight the Prophet. When the Prophet, still in Mecca, was informed about them he decided to march against them. He met them at Hunayn, and God, the Great and Mighty, inflicted defeat on them.
God has mentioned this battle in the Qur’an. Since they had marched with their women, children, and flocks, God granted them as booty to His Messenger, who divided the spoils among those Quraysh who had [recently] embraced Islam. …
When Malik [b. Awf] decided to march against the Messenger of God, he took with his men their possessions, wives, and children. After making camp at Awtas, the men gathered around him. Among them was Durayd b. al-Simmah, who was carried in a Howdah [Shijar].
As soon as he had encamped he inquired what valey they were in. When he was told that it was Awtas, he said: ‘What a wonderful place for CAVALRY! Neither a rugged hill, nor a soft lowland full of dust. …” 
Tafsir Ibn Kathir:
“The Battle of Hunayn
The battle of Hunayn occurred after the victory of Makkah, in the month of Shawwal of the eighth year of Hijrah. After the Prophet conquered Makkah and things settled, most of its people embraced Islam and he set them free. News came to the Messenger of Allah that the tribe of Hawazin were gathering their forces to fight him, under the command of Malik bin `Awf An-Nadri, as well as, the entire tribe of Thaqif, the tribes of Banu Jusham, Banu Sa`d bin Bakr, a few people of Awza` from Banu Hilal and some people from Bani `Amr bin `Amir and `Awf bin `Amir.
They brought their women, children, sheep and camels along, in addition to their armed forces and adequate supplies. The Messenger of Allah marched to meet them with the army that he brought to conquer Makkah, ten thousand from the Muhajirin, the Ansar and various Arab tribes. Along with them came the Tulaqa’ numbering two thousand men. The Messenger took them along to meet the enemy.
The two armies met in Humayn, a valley between Makkah and At-Ta’if. The battle started in the early part of the morning, when the Huwazin forces, who were lying in ambush, descended on the valley when the Muslims entered. Muslims were suddenly struck by the ambush, the arrows descended on them and the swords struck them.
The Huwazin commander ordered them to descend and attack the Muslims as one block, and when they did that, the Muslims retreated in haste, just as Allah described them. The Messenger of Allah remained firm in his position while riding his mule, Ash-Shahba’.
He was leading his mule towards the enemy, while his uncle Al-`Abbas was holding its right-hand rope and ﴿his cousin﴾ Abu Sufyan bin Al-Harith bin `Abdul-Muttalib was holding the left rope. They tried to hold the mule back so it would not run faster toward the enemy. Meanwhile, the Messenger of Allah was declaring his name aloud and saying, …” 
 Kitab Tabaqat Al-Kabir, By Ibn Sa’d, volume 2, page 185
 The History of al-Tabari: The Last Years of the Prophet: the Formation of the State
by Abu Ja’far Muhammad Bin Jarir Al-Tabari (Author), Ismail K. Poonawala (Translator), volume 9,
Page 2 – 4
 Tafsir Ibn Kathir, 9:26 verse, http://www.alim.org/library/quran/AlQuran-tafsir/TIK/9/25