If you're talking about getting the "Not enough citizens to complete this build!" pop-up when completing a Settler (or Worker), then choosing "Abandon city" will destroy the town, and give you a Settler (or Worker).
If you gave the tech and received the resource you do not loose your rep. I THINK the AI does in either case, but they always seem to be able to keep up so I am not 100% it actually applies to them.
It you give gold lump sum and there are no per turn deals this does not apply. If you are paying GPT for a tech then it does. If the AI declares war you are OK, it is the AI's fault (so you can abuse the "get out of my territory or declare war"). Anything else means you lose your rep, and cannot make GPT for tech trades (unless the AI you want to trade with is at war with the one you broke a deal with).
If the AI declares peace you are OK. If the alliance is broken by either you or the AI killing the target then I think you loose your rep.
In the game which I finished last night there was the tiny one-tile island civ of India which had such a bad relationship with France and me (Korea) -who had been forced to jointly conquer their dozen-city mainland- that they kept dragging everyone into wars (they were unconquerable because everybody was going for the spaceship victory and there were five scientific civs so nobody had developed amphibious warfare). It worked out for me because the Greeks beat me to building the United Nations but were at war with at least two nations at any one time, but still, dang were those Indians annoying.
If the AI-Leader ends your Alliance by eliminating the mutual foe, while you are still paying per-turn for an Alliance that has not yet run the full 20 turns, then surely that counts as them ending the deal? If so, your rep should stay intact.
tl;dr Korea didn't have Coal and France didn't have Dyes. The intervening lands which India held had both, and also India was superpower Persia's client/buffer state. All that was needed was to, as usual, just replace all the improductive swamps with barricaded forestlands to forestall Persian invasions. The danged Xerxes deserved it, because he could have built not one but two isthmus cities and screwed both locations.
An army takes one spot for each unit in the army and one foe the army itself. So if you want to transport a full army on a galleon, put two units in the army, ship it to the destination and add the other two units when it gets there.
