Though saltpetre was available from Chile frim the mid 19th Century, most of the munitions made until around 1900 used nitrates from urine or bird droppings.

When Chile became unavailable to Germany during WW1 (due to British sea dominance) they invented a method of capturing Nitrogen from the air (it's 80% Nitrogen) called the Haber process. This effectively replaced most other sources of nitrates for weapons as they could be provided in situ in large quantities.

The village where I live (Ashwell, Herts UK) had 2 very rewarding industries from Elizabethan times till the 20th Century. One was plaiting (braiding) straw for the Luton hat industry and the other was collecting pigeon droppings for gunpowder (urine was also collected, as it was in many places). These paid so well that the local farmers continually complained labour was far too expensive.

:-)
Ian