Khaybar is one of the famous Jihad against non-muslims done by Muslims during Muhammad's period.
Let's look at the reason behind why Muhammad wage a war against Khaybar residents.
Read the History of Al-Tabari Volume 8 (The Events of the Year 7 ) page 117, from this we get the reason behind the war.
check the highlighted words,
"Messenger of God, by God we have been struck by drought and possess nothing." But they found that the Messenger of God had nothing to give them.
So the Prophet said:
"O God, Thou knowest their condition-that they have no strength and that I have nothing to give them. Open to them [for conquest] the greatest of the fortresses of Khaybar, the one most abounding in food and fat meat."
Also read the next part,
There was no fortress in Khaybar more abounding in food and fat meat than it.
So the main reason to wage war against the people of Khaybar was to loot them to get what they have, mainly food and fat meat.
Another reason for attacking Khaybar can be seen in Sahih al-Bukhari 3701 which is also reported in Sahih al-Bukhari 3702 saying that this incident happened during the battle of Khaibar. This can be also read in Sahih al-Bukhari 3009 [beware of Taqiya in Translations]
Muslims are attacking Khaybar because they want people at Khaybar accept Islam, else they will be attacked. The first words Muhammad uttered was "Allah akbar! Khaybar is destroyed....." with his sword and his army. We will see that.
Now let's look at the how he loot Khaybar or how Muhammad invite them to Islam in detail.
Ibn Ishaq Sirat Rasul Allah - The Expedition to Kaybar A.H 7 - page 511
Muhammad waited until morning for the workers to awake from sleep to work in their fields so to attack them surprisingly. If you check Hadiths you can find that it was still dark in the morning (Sahih ~ Sunan an-Nasa'i 3380) when he attacked the innocent workers of Khaybar.
When the workers of Khaybar see Muhammad and his army, the innocent people cried and yell. They are innocent people and Muhammad and his army looted them because Sahabis (companions) don't have nothing to eat and Muhammad couldn't feed his own Sahabis (companions) as mentioned in al-Tabari.
Check the Sahih hadith ~ Sunan an-Nasa'i 3380, also note Sahih al-Bukhari 4197, Sahih al-Bukhari 4198
In this hadith, it says when Muhammad loot Khaybar it was still dark early in the morning, also Muhammad claims himself as EVIL.
When you read the History of Al-Tabari Volume 8 (The Events of the Year 7 ) page 122-123
Allah's apostle conqured PIECE BY PIECE the forts of Khaybar. And he took captives as sex slave for his Sahabis (companions). You can see that Safiya was one of the captives of war and she was taken by Muhammad'S Sahabi Dihyah for his NEEDS.
When you read the History of Al-Tabari Volume 8 (The Events of the Year 7 ) page 122-123
You can see the brutality of Muhammad murderring Kinanah husband of Safiya for his wealth.
Let's check how Muhammad got Safiyah in another post.
A brief summary can be found in History of Tabari - Volume 9 page:134-135
Now look at this hadith Sunan Abi Dawud 2967 and you may also read Musnad Ahmad 58
Muhammad take the booty from Khaybar. And he split into three sections, where two for muslims who fought and one for him and his family, AND IF SOMETHING remained after they have taken, it is given to the emigrants who accepted Islam and foight in the way of Allah.