وَٱلَّذِينَ كَفَرُواْ بَعۡضُهُمۡ أَوۡلِيَآءُ بَعۡضٍۚ إِلَّا تَفۡعَلُوهُ تَكُن فِتۡنَةٞ فِي ٱلۡأَرۡضِ وَفَسَادٞ كَبِيرٞ ٧٣
And those who disbelieved are allies of one another. If you do not do so [i.e., ally yourselves with other believers], there will be fitnah [i.e., disbelief and oppression] on earth and great corruption.
Translation: Saheeh International (English)
Each word's meaning and sound
The disbelievers are united in their disbelief and they therefore become friends of one another. A believer should not become friends with them. If you do not become friends with the believers and oppose the disbelievers, the believers will suffer weakness as a result of a lack of support and there will be great corruption on earth as people will be prevented from Allah’s path.
Al-Mukhtasar in interpreting the Noble Quran