Initially, Muhammad used to invite other tribes to Islam before attacking them. But later, he even abandoned this practice for the greed of pastures. 

For example, Muhammad suddenly attacked the tribe of Banu al-Mustaliq in 5 AH while they were completely unaware. 

Sahih Muslim 1730a:

Ibn 'Aun reported: I wrote to Nafi' inquiring from him whether it was necessary to extend (to the disbelievers) an invitation to accept (Islam) before meeting them in fight. He wrote (in reply) to me that it was necessary (only) in the early days of Islam. The Messenger of Allah (ﷺ) made a raid upon Banu Mustaliq while they were unaware and their cattle were having a drink at the water. He killed those who fought and imprisoned others. On that very day, he captured Juwairiya bint al-Harith. Nafi' said that this tradition was related to him by Abdullah b. Umar who (himself) was among the raiding troops.

Previously, Muslims would give other tribes at least 3 days to either accept Islam or be ready for annihilation. However, this time, in the greed for spoils of war, all ethics and principles were broken.

New principles were being established for looting, stating that all pastures and lands belong solely to Allah and His Messenger. Therefore, raiding any tribe while they were unaware became permissible, even if it meant the death of women and children.

Sunan Abi Dawud 2634:

Anas said “The Prophet (ﷺ) used to attack at the time of the dawn prayer and hear. If he heard a call to prayer, he would refrain from them, otherwise would attack (them).

Grade: Sahih (Al-Albani)

After stopping inviting tribes to Islam, Muhammad started attacking tribes during nighttime. 

Sunan Abi Dawud 2638:

The Messenger of Allah (ﷺ) appointed AbuBakr our commander and we fought with some people who were polytheists, and we attacked them at night, killing them. Our war-cry that night was "put to death; put to death." Salamah said: I killed that night with my hand polytheists belonging to seven houses.

Muhammad didn't even care if innocent women and children were also got killed during those night raids, but he didn't want to change his way (i.e. to give invitation first to give them a chance to accept Islam and in order to avoid killing of women and children).

Sahih al-Bukhari 2850 (Translate by Aisha Bewley):

باب أَهْلِ الدَّارِ يُبَيَّتُونَ فَيُصَابُ الْوِلْدَانُ وَالذَّرَارِيُّ

عَنِ الصَّعْبِ بْنِ جَثَّامَةَ ـ رضى الله عنهم ـ قَالَ مَرَّ بِيَ النَّبِيُّ صلى الله عليه وسلم بِالأَبْوَاءِ ـ أَوْ بِوَدَّانَ ـ وَسُئِلَ عَنْ أَهْلِ الدَّارِ يُبَيَّتُونَ مِنَ الْمُشْرِكِينَ، فَيُصَابُ مِنْ نِسَائِهِمْ وَذَرَارِيِّهِمْ قَالَ ‏"‏ هُمْ مِنْهُمْ ‏"‏‏.‏ وَسَمِعْتُهُ يَقُولُ ‏"‏ لاَ حِمَى إِلاَّ لِلَّهِ وَلِرَسُولِهِ صلى الله عليه وسلم ‏"‏‏.‏

CXLIV: The ruling about attacking the people of the Abode of War at night and thus striking infants and children

2850. It is related that as-Sa'b ibn Jaththama said, "The Prophet, may Allah bless him and grant him peace, passed by me at al-Abwa' or Waddan, and he was asked about attacking the idolaters of the people of the Abode of War at night when one might strike their women and children. He said, 'They are part of them (i.e. idolators).' I heard him (also) say, 'There is no hima حِمَى [i.e. protected pastured lands] except that of Allah Almighty and His Messenger.'"

hima حِمَى has not been correctly translated in English by the translators (either by 'Aisha Bewley or by Sunnah.Com). But we can see this exact meaning of 'pasture' in the Urdu Translation

Thus, Muhammad got hands to all pasture lands, and didn't give any share to his Jihadist companions. In order to understand this issue more, please read the article: The Story of War Booty: How Muhammad got more and more share from it?

Collateral Damage:

Today, America conducts drone attacks on Taliban terrorists, and the innocent people killed along with the terrorists are termed 'collateral damage.' However, Muslims do not accept America's theory of 'collateral damage.' But can these same Muslims reject their Prophet's theory of collateral damage, or will they justify the killing of women and children for pastures?

Yes, Muhammad could have easily avoided it:

  • If Muhammad had continued inviting those tribes to Islam before attacking them and given them 3 days to ponder upon it.
  • If Muhammad had not conducted night raids. Attacking during the daytime (when they would be unaware) would have also avoided the killing of women and children.

There is another difference between America and Muhammad. America, after occupying Afghanistan, neither enslaved anyone nor officially allowed its forces to rape any woman. However, Muhammad not only killed women and children during night raids but also enslaved the remaining women and even small children for their entire lives. And he also officially allowed his male companions to rape all women.

Response by Islamic Apologists:

In response to this objection, Muslim apologists claim that:

  • The Prophet never attacked pagan tribes as part of offensive Jihad, but he attacked only those pagan tribes who conspired against Muslims. 
  • Thus, the prophet attacked Banu al-Mustaliq, while they wanted to attack Muslims. 
  • And the prophet didn't attack them when they were 'unaware'. 
  • They never answer why their prophet enslaved all women and even small children for their entire lives, although they were fully innocent. 

They present the following tradition from Tabaqat Ibn Sa'd (link):

The Banu Mustaliq were from Khazaa (an ally tribe of Muslims).... The chief of Banu Mustaliq was Al-Harith bin Abi Dirar. He invited his people and the Arabs to fight against the Prophet. They agreed and prepared to march with him. When this news reached the Prophet, he sent Buraydah bin Al-Haseeb Al-Aslami to investigate. He confirmed the news upon his return (that Banu Mustaliq was planning an attack). The Prophet then prepared an army and set out.... Al-Harith bin Abi Dirar and his companions learned of the Prophet's march and that their spy had been killed by the Muslims. They were frightened and fled.... The people of Al-Muraisi fought but were scattered by the Muslim attack, with ten of them killed and the rest captured as slaves (and a large amount of spoils was obtained). Ibn Umar narrates that the Prophet attacked them while they were unaware and watering their livestock.... But the first narration is more established.

Our Response:

This narration by Ibn Sa'd is the sole narration on which Muslims base their claim that Banu al-Mustaliq was plotting with the Quraysh, which is why the Muslims attacked them. However, it is well established that the attack was not due to any conspiracy but out of greed for pastures, and thus Muhammad stopped even inviting the tribes to Islam and started attacking them during night raids when they were totally unaware. 

Ibn Sa'd claims that his narration is more reliable than the narration by Ibn Umar (which is also present in Sahih Bukhari), which clearly states that the people were unaware of any Muslim attack.

Hafidh Ibn Hajar Al-Asqalani refutes Ibn Sa'd's claim in his book Fath al-Bari and states:

The narrations in Sahih Bukhari and Muslim are given precedence over other historical narrations (like that of Ibn Sa'd).

Reference: Seerat-un-Nabi, Syed Sulaiman Nadvi, page 238.

Conclusion:

The narration of Ibn Umar is clear that the attack was carried out while they were completely unaware. The principle of inviting for three days before attacking was abolished. The reason for the attack was not any conspiracy with the Quraysh but solely the desire to acquire pastures.

Is this really the divine humanity we are asked to believe in?