What is the basis of launching Jihād against other countries? Are we required to fight them merely because they are non-Muslims or is there another reason for it?

As explained in a previous query1, fighting non-Muslims into subjugation was the prerogative of the Prophet Muhammad (sws) and his Companions (rta) only. It was actually a form of divine punishment meted out to people who had deliberately denied the truth. After their departure, according to the Qur’ān, the only legitimate reason for an Islamic state to undertake Jihād is to curb oppression and persecution in some other state whether Muslim or Non-Muslim. The Qur’ān says:

وَمَا لَكُمْ لَا تُقَاتِلُونَ فِي سَبِيلِ اللَّهِ وَالْمُسْتَضْعَفِينَ مِنْ الرِّجَالِ وَالنِّسَاءِ وَالْوِلْدَانِ  الَّذِينَ يَقُولُونَ رَبَّنَا أَخْرِجْنَا مِنْ هَذِهِ الْقَرْيَةِ الظَّالِمِ أَهْلُهَا وَاجْعَل لَنَا مِنْ لَدُنْكَ وَلِيًّا وَاجْعَل لَنَا مِنْ لَدُنْكَ نَصِيرًا(٧٥:٤)

And why is it that you not fight in the cause of God and for the cause of those who, being weak, are ill-treated and oppressed – men, women, and children, whose cry is: ‘Our Lord! rescue us from this town, whose people are oppressors; and raise for us from unto You one who will protect and raise for us from unto You one who will help!’ (4:75)

In other words, to fight for the defence of the weak and the oppressed is something which the Qur’ān upholds as the only valid reason for an Islamic state to wage war. Whether a particular people are oppressed and subjected to persecution and injustice is something which the elected representatives of the Muslims must themselves decide keeping in view the data they have.

Also, countries that have signed the UN charter are bound in a no war pact with all the member nations. So if ever a situation comes when they have to wage Jihād, they must first openly annul this pact, and of course be ready to face its consequences as well.

1. ‘Waging War against the Disbelievers’