What are the practical steps to take or what activism is necessary to Establish an Islamic leadership on the lines of the first few leaders of Islamic Ummah namely Muhammad pbuh, AbuBakr RA, Umar RA, Ali RA, Hasan RA, Hussain RA ...? Are some organizations already doing it ? if yes who are they?
Muslims need to adhere to Islam. http://www.youtube.com/watch?v=BXSOGCFaVfQ
In Muslim countries, democracy is a big thing preventing caliphate. Also sometimes there are big non-Muslim populations which the Muslims want to keep happy etc.
If all Muslims suddenly adhered strictly to Islam there wouldn't be much problem making a caliphate inshaAllah.
Establishment of the Caliphate is something that every Muslim dreams of especially when we contrast the inequities of the present times against the Golden Age of Islam and the justice that prevailed then.
From my own experience there are two camps that advocate two radically different approaches based on where they are ideologically grounded: while one camp says that we will get Caliphate only when we all become righteous, each and every one of us; the other camp takes an active approach of using democratic means to establish a "Caliphate," though it is doubtful if they will ever succeed in this endeavor. In Islam, the end -- no matter how noble -- will never justify the means.
We have to bear in mind that it is an impossible eventuality that the entire ummah will suddenly become righteous. This just isn't possible, and forwarding arguments like "we will get the Caliphate when the Masajids are as full during Fajr salaah as they are during Jumu'ah" are both self-defeating and discouraging.
On the other hand, neither is it advocated that we use the methodology of first trying to gain power, by whatever means like elections and so forth, and then bring about the Caliphate through an "Islamic revolution" that precedes it (if at all using such radical terms is even proper in the case of Islam). Both these mindsets may not be correct.
Rather, you will always there is a core group of people who first reform themselves and then carry on the task of Amr bil Maroof wa Nahi Anil Munkar, that is, reformation of other Muslims in general. These same people will eventually form the core of the future Islamic leadership, when it does come about by Allah's Will.
Secondly, we have to realize that we humans devise our own plans and Allah has His Own Plans, and His Plans supersede all other plans. So the best bet is that, even if we do not do direct dawah or otherwise do any kind of reformative work like calling people to good and preventing them from evil, we should always assist those who are doing this noble task, either morally or financially, so that they are free to carry on their work without any hindrances.
Insha Allah, when the time is ripe and Allah wills that the Caliphate be established, Allah will give the mantle of Caliph to whom He wills.
We do our work to the best of our abilities and Allah will Will what He plans to Will and none can force Him.
It has been already established, and it's divinely ordained. You'll just have to look around you. One of the proofs is this verse 55:33
tell me who has conquered the skies and the heavens and i'll tell you who has divine authority to rule the humans.
additional side note: what we need to revisit is the understanding of the meaning to be a muslim, what constitutes a civilization to be qualified as an islamic civilization if the currently rulling the world isn't "islamic" as conventionally undestood, perhaps we need to revisit the understanding of the conventional wisdom as it does not reflect the factual and authorized circumstances..
The main problem with a caliphate is that one person needs to be in charge and that is never going to happen. Ideally it would be under the Ottomans but they have little interest and no Sunni will ever agree with a Shia so the first thing to happen would be an internal civil war. Islam as a force is dead. It doesn't even make any of it's own weapons.