Ruin, havoc, devastation, destruction are comparable when they mean the bringing about of disaster or what is left by a disaster.
They are general terms which do not definitely indicate the cause or the effect yet suggest the kind of force operating to produce the kind of disaster involved.
Ruin implies generally a falling or tumbling down and is applicable to anything that through decay, corruption, neglect, or loss is unable to maintain its wholeness or soundness and so gives way or falls apart; this idea underlies all of the many uses of the word.
Havoc suggests an agent that pillages, despoils, or ravages and brings confusion and disorder with it.
Devastation basically implies a laying waste, usually of a widespread territory (as by war or a natural catastrophe), but it also is applicable to something (as disease) that overwhelms the individual or his property or resources like a natural catastrophe.
Destruction implies an unbuilding or pulling down or apart, but, since it is used alike of material and of immaterial things, it may suggest not only demolition but a killing, an undoing, or an annihilation; also, although it often connotes a conscious attempt to pull down, it as often suggests rather an inevitableness or an irony in the effect produced.