"Many British commentators have asked in surprise why India is being targeted. There is no confusion among Indians themselves. When the terrorists say on their websites that they seek to break up India and reclaim it for Islam, they speak a language many Hindu Indians understand." [from this article]
They wish to "reclaim India for Islam." India, and Israel, and Greece and the Balkans, and Bulgaria, and Rumania, and much of Hungary, and most of the Caucasus, and much of southern Russia, and almost all of Spain, and Sicily, and every place where Islam once dominated and Muslims ruled.
But that's not the end. That's ony at the top of the Muslim To-Do List. The Qur'an, the Hadith, the Sira do not teach Muslims to think that "Islam must rule wherever it once ruled, but every other place must be left alone." No. That would make no sense. Allah did not say that only part of the world belonged to him -- that part which Muslims had once held, up to this or that year. No, the entire world belongs to Allah. All of its land, all of its many lands, must ultimately have every obstacle to the spread, and then the dominance, of Islam removed.
There is the immediate To-Do List: India, Israel, Spain, the Balkans, and so on. And then there is the other list which simply reads: Everywhere else.