By brother Tripoly sunni:

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السؤال: هل الجهاد في سبيل الله واجب ؟
الجواب: الجهاد مع المعصوم (علیه السلام) أو نائبه الخاص واجب وهو حكم شرعي.]

Question (1): Is Jihad in the cause of Allah an Obligation upon Muslims?
Answer: Jihad with the infallible PBUH or his special representative is an Obligation and a Hukm in Sharia.

http://www.sistani.org/local.php?modules=nav&nid=5&cid=117

So According to him  jihad against the occupiers is not an obligation upon any Muslim unless the MAHDI appears or one of his 4 emissaries who died 1200 years ago.