After their unmitigated victory in A New Hope, the Rebel Alliance is once again in dire straits.
Three years after the destruction of the Death Star, this small, ragtag force has been forced into hiding, eventually settling on the remote, harsh planet of Hoth. Not exactly a great situation. To make things worse, the film opens with the Empire deploying probes in the hopes of locating this secret base and getting their revenge for the destruction of the Death Star.
In other words, the Empire is about to strike back. In addition to explaining the literal situation in the film, this title also gives us a hint that this is going to be a darker, heavier affair than the first film. The good guys may have found themselves A New Hope, but they better get ready before The Empire Strikes Back.