In the fourth verse (57), Allah Ta` ala has given a standing instruction to His Rasul ﷺ about such evil breakers of solemn pledges in the following words:

فَإِمَّا تَثْقَفَنَّهُمْ فِي الْحَرْ‌بِ فَشَرِّ‌دْ بِهِم مَّنْ خَلْفَهُمْ لَعَلَّهُمْ يَذَّكَّرُ‌ونَ ﴿57﴾

So, if you find them in war, make them an example (deterrent) for those behind them, so that they take a lesson.

Here, the word: تَثْقَفَنَّهُمْ (tathqafannahum) means to get the upper hand against them and the word: شرّدَ (sharrada) is a derivation from the infinitive noun: تَشرِید (tashrid) which essentially means to drive out or scatter away. So, the verse means: 'If you overpower such people in a war, give them a drastic punishment which becomes an instant lesson for others - so that those who are busy bashing Islam behind the cover of such people serving as their agent provocateurs should understand clearly that there remains no alternative for them but to run for their lives. The drive of the instruction is that these people should be punished in a manner which makes an impression on the disbelievers of Makkah and other hostile tribes and sucks away any courage they may have to come back and confront Muslims in the future.

By saying: لَعَلَّهُمْ يَذَّكَّرُ‌ونَ (so that they take a lesson - 57) at the end of the verse, a hint has been given towards the universal mercy of the Lord of all the worlds. This treatment makes it clear that the real purpose of this exemplary punishment was not to take revenge or release personal anger, in fact, this was being awarded in their own interest and expedient gain whereby they may, perhaps, review conditions before them, regain some of their sanity, feel ashamed of what they did and go on to correct themselves.