What are the circumstances that make Jihād obligatory? What is the punishment for not taking part in Jihād when it has become obligatory?
Answer: The first part of your question can have two aspects:
i. When does Jihād become obligatory on a state?
ii. When does Jihād become obligatory on an individual?
As far as the first aspect is concerned, the answer is that Jihād becomes compulsory on a state if in the opinion of its rulers it has the military and moral might to curb the oppression and injustice1 of the country against which Jihād is to be waged. This inference is based on the guidance provided by the Qur’ān to the Prophet (sws) and his Companions (rta). They were told that if they possessed a certain level of military strength (ie number of combatants), it was imperative upon them to wage Jihād. This principle is spelled out in the following verses:
يَاأَيُّهَا النَّبِيُّ حَرِّضْ الْمُؤْمِنِينَ عَلَى الْقِتَالِ إِنْ يَكُنْ مِنْكُمْ عِشْرُونَ صَابِرُونَ يَغْلِبُوا مِائَتَيْنِ وَإِنْ يَكُنْ مِنْكُمْ مِائَةٌ يَغْلِبُوا أَلْفًا مِنْ الَّذِينَ كَفَرُوا بِأَنَّهُمْ قَوْمٌ لَا يَفْقَهُونَ الْآنَ خَفَّفَ اللَّهُ عَنكُمْ وَعَلِمَ أَنَّ فِيكُمْ ضَعْفًا فَإِنْ يَكُنْ مِنْكُمْ مِائَةٌ صَابِرَةٌ يَغْلِبُوا مِائَتَيْنِ وَإِنْ يَكُنْ مِنْكُمْ أَلْفٌ يَغْلِبُوا أَلْفَيْنِ بِإِذْنِ اللَّهِ وَاللَّهُ مَعَ الصَّابِرِينَ(٨: ٦٥-٦٦)
Prophet! Rouse the believers to wage war. If there are twenty amongst you, patient and persevering, they will subdue two hundred: if a hundred, they will subdue a thousand of the Disbelievers: for these are a people without understanding. [From] now, God has lightened your [task] for He knows that there is now weakness amongst you: But [ever so], if there are a hundred of you, patient and persevering, they will subdue two hundred, and if a thousand, they will subdue two thousand, with the leave of God: for God is with those who patiently persevere. (8:65-6)
It is evident from these verses that the Prophet (sws) and his Companions (rta) were required to fight if they were outnumbered by 1:10 and later by 1:2 because it was their inner strength – the strength of faith which would compensate for their numbers. However, since these ratios specifically pertained to the Companions (rta) whose level of faith one can only imagine, in later times the rulers must exercise their judgement in working out a ratio for themselves. What can be said with certainty is that Muslim to enemy ratio should be at least 1:2.
Of course, a natural pre-condition to waging Jihād is that all diplomatic level negotiations have failed.
As far as an individual is concerned, Jihād becomes compulsory upon him if both the following conditions are fulfilled:
i. The rulers give a call to each an every citizen of their country to participate in Jihād.2
ii. The individual himself is convinced that his rulers are waging war on the only legitimate basis on which war can now be waged: to uproot injustice and oppression perpetrated by a country. If a person is convinced that his country has some other objective in mind, he can of course refuse their call.
Now I come to the second part of your query:
A study of the Qur’ān shows that there is no worldly punishment for either a state or an individual if they do not undertake Jihād when it becomes obligatory upon them. The reason for this is that the Qur’ān does not mention any such punishment. It seems that it is the Almighty Himself Who directly punishes such negligence in this world or in the Hereafter.
1. According to the Qur’ān (4:75), this is only the legitimate reason for an Islamic state to wage Jihād today.
2. According to the Qur’ān (9:38-9), in the Prophet’s times, such a call was given by the Islamic state to the each and every Muslim before the battle of Tabūk.