Haldeman's 1974 story follows a group of soldiers, but in particular William Mandella and his friend Marygay, conscripted into the military following an attack on human colonies by the alien Taurans. After gruelling training on Earth, he and his companions are sent through a wormhole type phenomenon to fight – but the vast distances involved mean that each time they return to Earth, decades or centuries of local time have passed and society has massively changed, even though the soldiers have only experienced weeks or months of subjective time.
It's certainly got big concepts at its core, but audiences might be more ready for them thanks to exploration of wormhole mechanics in Christopher Nolan's Interstellar (2014) and the effects on time.
Other key players here besides Tatum are Richard Edlund, a visual effects artist who worked on (among many other things) the original Star Wars trilogy and who owned the rights, plus Prometheus (2012) writer Jon Spaihts, who is attached to provide the script. Can The Forever War finally be won? We may finally find out.