“THE EXPEDITION TO QUTBA B. AMIR AT AL-KHATH’AM IN SAFAR YEAR NONE AH
… Ibn Ka’b b. Malik related to us that the Prophet sent Qutba b. Amir b. Hadida with twenty men to the tribe of Khatham in the region of Tabala. He ordered him to raid them and to march by night and hide by day, and to hurry the march. So they set out with ten camels taking turns on them.
They hid their weapons. They went along a crack until they reached Batn Masha. They captured a man and asked him, but could not understand his language, and he immediately began to shout. …” 
The historical sources for the expedition of Qutbah Ibn Amir to the tribe of Khath’am, doesn’t give us much information why it took place. Dr. Shawqi mentions that a fighting took place. Dr. Shawqi Abu Khalil:
“The expedition of Qutbah Ibn Aamir to Tabalah in Safar 9 Ah. This is where the tribe of Khat’am were, towards Bashah, near Turabah. Fighting took place between the Muslims and Khath’am.” 
Whereas Talib Jaleel, informs us that they were rebels who were fought against.
“In Safar, 9H a jamat led by Qutbah bin Amir to Tabalah, to reign on some rebels. The enemies were fought and brought back to Madeenah.” 
Moreover, Dr. Ali Shehata Abdou Selim gives us a little more information that this tribe continually persecuted Muslims. And as result of this, the Prophet (p) sent out his companions to deal with the oppressors:
“Some members from the clan of Khath’am suffered severe persecution as a result of their embracing of Islam. They filed a complaint to the Prophet Muhammed, peace be upon him. In response, the Prophet Muhammed, commanded the Muslims of Khath’am to migrate to Medina. At that time migration was an Islamic obligation. Nevertheless, the Muslim members of the clan of the Khath’am did not migrate.
A Muslim armed group was commissioned to respond to the persecution practised by the disbelievers from the clan of Khath’am. This Muslim group was unable to distinguish between the persecuted Muslims and the oppressors of Khatham, so they hurt Muslims by mistake. …” 
This makes clear sense. The Prophet (p) never attacked anyone who was at peace with the Muslims. In fact, the Prophet (p) in a famous Hadith urges God Almighty to only use his ‘revenge’ against those who oppress innocent people:
“O GOD! let us enjoy our hearing, our sight and our power as long as You keep us alive and make our heirs from our own offspring, and make our revenge RESTRICTED TO THOSE WHO OPRESS US, and support us AGAINST THOSE WHO ARE HOSTILE TO US let no misfortune afflict our Deen; let not worldly affairs be our principal concern, or the ultimate limit of our knowledge, and let not those rule over us who do not show mercy to us.” (Riyad as-Salihin Book 5, Hadith 834)
From the above authentic Hadith, we gather that the Prophet’s (p) number one goal in life was to only fight those who persecuted innocents. If they left Muslims to preach, have a free life where they don’t get attacked for their beliefs, then such tribes or countries were never touched.
Fighting the enemy only started when innocent lives were in danger or tyrants oppressed them and hence the Prophet (p) would have sent out his people to deal with such criminals, 1400 years ago.
 The Life of Muhammad: Al-Waqidi’s Kitab Al-Maghazi [Translator: Rizwi Faizer] page 481
 Atlas On The Prophet’s Biography, Places, Nations, Lanmarks (‘Al-sirah Al-Nabawiyah’), By Dr. Shawqi Abu Khalil, page 235
 Notes On Entering Deen Completely: Islam as its followers know it, by Talib Jaleel, page 510
 The Concept of Coexistence in Islamic Primary Sources: An Analytical Examination By Dr. Ali Shehata Abdou Selim, page 51 – 52