A theoretical War...
The war on entropy corresponds to the ongoing battle aiming to bring about an energy efficient future fueled by clean, renewable sources. Entropy is a state of thermodynamics that always increases, particularly in any interaction where heat is a byproduct. Thus, the most inefficient ways to use energy, all involving combustion, contribute the most entropy to the world. The war on entropy strives to provide the same services to people more efficiently, thereby minimizing entropy.
If you want to bridge the philosophical <—>concrete gap of the war on entropy, read about mining your own time.