You are right that when Ameer (ruler or head of state) declares Jihad, it becomes general call for Jihad, but even then it depends on type of war and requirement of Ameer. Some wars are not Jihad. Further, even if war is Jihad, Ameer can decide what to do, entirely depend on standing army or make general call. Anyhow, whoever gets enrolled by Ameer does Jihad. Rest, who are not enrolled, their fards get fulfilled by those who take part in Jihad (and that is why this Jihad is not fard but fard-e-Kifaya).
Please let me go through a bit in detail (according to my knowledge and understanding) so to put things straight. I will ask you question later in this post. Fard is duty and responsibility.
Fard-e-Ayn is fard that are related to personal life of an individual and individual’s duty towards people who are individual’s responsibility.
Fard-e-Kifaya is fard on ‘group gathered’ or ‘nation (Ummah)’ but not fard on each and every individual.
Jihad (by sword) is related to life of nation (ummah). Such Jihad is responsibility of ruler (Khalifa, Ameer, or head of state). Ruler fulfils this responsibility with the help of nation. All such responsibilities that are fard on ruler are fard-e-Kifaya on individuals.
Anyhow, as far as Jihad (by sword) is concerned, ruler cannot start an unjust war (war of aggression) and expect that it is Jihad. Similarly, individuals if they believe that war of ruler is unjust than to take part in such war is not fard (war of aggression is war of sinners).
War that are fard if declared by ‘head of state’ (Ameer or ruler):
1: Defensive war (defending against aggressors)
2: War of retribution (if war is in response to past aggression or past unjust result)
3: War imposed (due to threats by others).
War that is not fard rather sin (even if head of state declares that war):
1: War of aggression are wars to expand territory or for loot and plunder.
2: War for aggression in the name of religion (Islam) for conversion:
[Note: war in the name of religion for conversion is nothing to do with Islam. Actually, Islam even forbids conversion of people who got occupied by Muslims due to just wars. In Islam, these occupied non-Muslims are left to follow their own religion and it is they who could decide to accept Islam willingly if they want to].
Reasons Jihad (by sword) is not fard on individuals but becomes fard-e-Kifaya when state calls people to join Jihad.
If Jihad would have been fard on individuals, then everyone within a state according to their understanding or understanding of their guru (so-called religious scholars) would have started Jihad on others. Such would only create fitna and not jihad.
For instance … let see some scenario of Jihad not decided by state but by people (considering Jihad as fard and not fard-e-Kifaya):
1: Let say, I with group of like minded Pakistanis on our own or under the influence of some so-called ‘religious scholar’ decide that it is fard Jihad on me to fight ‘India or USA’ and we attacked ‘India or USA’ on our own (to fulfil that fard). The consequence of such attack could be retaliation (war and/or sanctions). Such retaliation may not only effect like minded us, but would affect whole nation (Pakistanis) whose responsibility is not ours but it is of state (people ruling). It is also state who is answerable of their well being to Allah, and not we. So, we not only interfered with duty and responsibility of others (state), but with our actions we endangered life of many innocent people.
2: Let say, I with group of like minded Pakistanis on our own or under the influence of some so-called ‘religious scholars’ decides that it is fard on us to do Jihad and clean Pakistan from deviant sects (what is happening a lot in Pakistan in name of so-called Jihad by Kharjees). Suppose in our dictionary Wahabis and Deobandis are that deviant sects. So, we start killing all ‘Wahabis and Deobandis’ in Pakistan. Start target killing known Deobandi ulemas like Taqi Usmani and others, start blowing Deobandi mosques, Deobandi madrasas, Raiwand gatherings, and so on. In process, many innocent would get killed and affected and we would create fear in the hearts of people following Deobandi sect.
3: Let say, if we consider such Jihad mentioned above (1 and 2) as fard on us, and start donating money to people doing what is mentioned above, or helping them with moral support or in whatever way we can, then also we would be doing same what above two groups would be doing.
Now … what you think? Are the above mentioned Jihad fard or Fitna?
To me, all above 3 hypothesis I mentioned (actually, they are not hypothesis but is actually happening in Pakistan, though instead of Deobandis it is Shias and Brelvies) are Fitna and all people involved in such actions what they claim as Jihad are Kharjees who would end up in hell.
What you think of such so-called Jihad?
1: Do you think it is Jihad to start attack on other countries without state involvement?
2: Do you think it is Jihad to kill people following Deobandi sect (or any sect)?
3: Do you think it is Jihad to help such groups attacking and killing others with money, moral and other supports?
Please reply to above three questions.