Whatever its equipment, a military is nothing without its people. As many militaries struggle with recruitment, the armies in Ukraine grow older, and countries in Asia grapple with the implications of ageing populations, it's becoming clear that getting the right people may be as much of a challenge for forces as getting the right technology. So today, we look at that age old problem. How do militaries get people, why are so many struggling - and what might they be able to do about it?