These phrases refer to any cities that sent out large numbers of soldiers. Alternate translation: "Cities that went out with a thousand ... cities that went out with a hundred" (See: [[rc://en/ta/man/translate/figs-genericnoun]])
"The city that went out" represents the soldiers of that city going out. It can be stated clearly why they went out. Alternate translation: "The city out of which a thousand soldiers went to fight" or "The city that sent out a thousand soldiers to fight" (See: [[rc://en/ta/man/translate/figs-explicit]])
"will have a hundred soldiers who have not been killed" or "will have only a hundred soldiers still alive." Here being "left" refers to not being killed by the enemy.