[siunevada]

return to a single Islamic state, known as "the Caliphate,"

'Return' implies they attained this status in a past age. Close. But there never has been a unified single Muslim entity under a caliph.

Good luck unifying those Sunni and Shia.

[Restorer]

But there never has been a unified single Muslim entity under a caliph.

Not actually true. The original unified Muslim state under the first caliphs lasted till about 750, so well over 100 years. They have not, however, come close to reestablishing a unified caliphate since.