The easy way to relive the Empire Strikes Back story in the Galactic Conquest mode is to choose the Rim World Conflict scenario (as the Empire). In that scenario, the Consortium will be pretty easy to beat, so focus on them first even when upgrading through tech levels. After that, the Battle of Hoth and the Bespin subjugation (which composed the whole story of ESB) will be relived (only if those planets are saved for last).