The biggest threat to ammo is moisture. Store it in a sealed container, preferably with dessicant if the container has been opened. Do not store the ammo in locations where there might be high humidity such as in rooms with washers, dryers or water heaters ( in case of a leak ) I prefer ammo with a recent date of manufacture but like the others I have shot WWII ammo with no problem. I have bought, sold and shot ammo from China, Mayalasia, Russia, Yugoslavia, Mexico and who knows where else with no problems. As MaxPF noted lots of the older ammo is corrosive so be aware and clean appropriately if shooting the older ammo. I have a lot of ammo, some I bought new 20 years ago, some is vintage ammo like Lake City Match and some is old WWII stuff. All have performed flawlessly. I also used to load lots of ammo and I still have ammo that I loaded 15-20 years ago that shoots like new.