actually in Ireland I believe point (1) was a huge contributor:  the best land was reserved for cash-cropping for staples exported to England, iirc.  Ireland was operated as a colony of England, with English landlords supervising hacienda agriculture and the indigenous (so to speak) Irish dispossessed and shuffled off onto the worst, most marginal land.

the potato (a New World crop brought back by the colonisers whose journeys were in part funded by the super-profits obtained by disposession and Enclosure) was touted as the solution to the "Irish problem" -- land too poor to support wheat/beef (high prestige) farming would support potatoes (which when mixed with dairy form a remarkably nutritious diet)... anyway, the history of the Irish famine is too long and complicated for a drive-by post but colonial cash-cropping was definitely a big part of the big picture.  someone must have more recent reading in the history of the Troubles than mine, and can fill in the gaps?

The difference between theory and practise in practise ...