How does the world defeat ISIS, and terrorism in general?

Nu’aym ibn Hammad narrates in Al-Fitan, that the 4th Caliph, Ali ibn Abi Talib said:

When you see the black flags, remain where you are and do not move your hands or your feet. Thereafter there shall appear a feeble insignificant folk. Their hearts will be like fragments of iron. They will have the state. They will fulfil neither covenant nor agreement. They will call to the truth, but they will not be people of the truth. Their names will be parental attributions, and their aliases will be derived from towns. Their hair will be free-flowing like that of women. This situation will remain until they differ among themselves. Thereafter, God will bring forth the Truth through whomever He wills.

This hadith is used to justify ISIS/ISIL. According to this letter found on

http://lettertobaghdadi.com/

there is possibly another understanding of this hadith:

When you see the black flags

The flags of the ‘Islamic State’ are black.

Remain where you are

i.e., stay where you are, O Muslims, and do not join them.

And do not move your hands or your feet

i.e. do not help them financially or with equipment.

Thereafter there shall appear a feeble insignificant folk

i.e. ‘weak’ and ‘insignificant’ in terms of understanding of religion, morality and religious practice.

Their hearts will be like fragments of iron

i.e. they will ruthlessly kill prisoners of war and cruelly torture people.

They will have the state

For almost a century, no one has claimed to be an Islamic Caliphate other than the current ‘Islamic State’ in Iraq and the Levant.

They will fulfill neither covenant nor agreement

The ‘Islamic State’ did not fulfill its agreement with the Sha’etat tribe after the tribe pledged allegiance to them; indeed the ‘Islamic State’ slaughtered them by the hundreds. They also killed journalists.

They will call to the truth

The ‘Islamic State’ calls to Islam.

But they will not be people of the truth

The people of the truth are merciful. The Prophet Muhammad said: ‘Have mercy and you will be shown mercy.’

Their names will be parental attributions Like: ‘Abu Muthanna’, ‘Abu Muhammad’, ‘Abu Muslim’ and so on.

And their aliases will be derived from towns Like: ‘Al-Baghdadi’, ‘al-Zarqawi’, ‘al-Tunisi’ and so on.

Their hair will be free flowing like that of women

Islamic State’ fighters have hair precisely like this.

Until they differ among themselves Like the differences between the ‘Islamic State’ and its parent, the al-Nusra Front (al-Qaeda in Syria). The fighting between these two has led to around ten thousand deaths in a single year.

Thereafter, God will bring forth the truth through whomever He wills

through a clear and correct Islamic proclamation.

/r/AskReddit Thread