There was something I was going to say in my previous post about India's warning over Sikh extremists in the UK but didn't because of a lack of time.
The phenomenon of ethnic diasporas supporting extremists back in there homeland is not unusual, as well as Sikhs and Tamils that I mentioned in the previous post there are also examples like the support for the IRA from plastic paddies in the USA and support for the Nazis by the German American Bund and so on. If a country takes a large number of immigrants from a volatile part of the world then it is quite likely that they will become involved in that conflict to some extent. This also one reason why the problem of Islamism is so different and potentially hard to defeat compared to the others.
If a Sikh in the West is an alienated loser and wishes to channel his self pity into supporting terrorism there is only one potential outlet* for him to identify with, the struggle of Sikh separatists in India. Once that conflict is resolved the aforementioned oddball has nowhere to channel his loserness.
However with an alienated Muslim loser there are dozens of conflicts for him to whet his self pity with from Sudan to Israel/Palestine to Kashmir to Thailand to the Philippines. It is almost impossible to resolve all of these conflicts, so there is almost always some grievance that can be nurtured. This will remain the case for as long as it is considered normal and acceptable to show solidarity for overseas groups based purely on their ethnic background.
* I realise that in theory they could identify with ideological terrorism like the various far left groups that infested Europe and the USA during the 1960s and 70s, but in reality these groups never seem to attract a broad swathe of support and tolerance so their support has remained confined to a tiny slither of the spoilt offspring of the very rich. Most major terrorist groups are based around ethnic identity.
44 minutes ago