My reply to Bill Moore's question (Post 37):
what significant change and challenges do you think we would face with our FID doctrine if the focus shifted from the rural to the urban?
I was not thinking of just the USA intervening and my SWC reading does not make me familiar with US FID doctrine. Caveats aside here goes.

An urban setting for an insurgency / terrorist campaign absorbs manpower like a sponge, so using and adapting a local security element to the 'sepoy model' makes a lot of sense. You referred to 'The Troubles' in Northern Ireland (1969-1998), at one stage the UK had 30k soldiers there - Operation Motorman, when police primacy had not been reached. Nearly all of them in two cities, Belfast & Londonderry.

Secondly by time FID is deployed the host nation will have lost considerable control and governance will be weakened. Think of the favelas in Rio and some "no go" areas elsewhere. Citizen involvement in providing information to the state will be low, especially if intimidation is prevalent - not necessarily violent nor observable. In one period in 'The Troubles' Loyalists used cameras without film to intimidate; imagine the impact today of mobile-phones.

F3EA will be problematic until many other factors act as enablers: informants, intelligence, surveillance etc. Enough time may not be given.

Pinpoint accuracy of weapons systems, especially the use of explosives, will be limited in densely occupied spaces. They might not even be allowed by the host.

Finally image is important, even crucial. Not for the 'armchair" observers, but the people affected by the presence of FID-users. It simply is a very different image if the security forces appear similar, even if with a few expatriate officers & NCOs.