Fulfil the Covenant of Allah when ye have entered into it, and break not your oaths after ye have confirmed them; indeed ye have made Allah your surety; for Allah knoweth all that ye do
It was common for the Arabs to ally with one another, through swearing an oath of loyalty, for the gain of a temporary advantage. If they thought they would be more powerful by canceling their current alliance and allying with another group, they would. Thus, they made their oaths a joke. This verse forbids this misuse of oaths in making alliances. In fact, the Prophet eventually forbade the making of oaths for any other purpose than personal goals. He said, “There is no oath-making (for political alliances) in Islam, and any oaths made in the days of ignorance are only reinforced in Islam.” (Ahmad) In other words, making personal pacts between non-governmental groups is forbidden, unless they were made before Islam’s coming, in which case they must be honestly observed. Personal vows and formal political treaties between governments are, of course, exempted from this ban.
Emerick, Yahiya. The Meaning of the Holy Qur’an in Today’s English (p. 829). Unknown. Kindle Edition.