Paraguay has a long history of stupid wars. They started the Chaco War with Bolivia over control of the Chaco region, which they thought was full of oil. Turns out it wasn't and it it's mostly uninhabited forests with some Mennonites now.
There's rich mineral/gas deposits. Also the part that we lost to Bolivia does contain oil. Also with fracking probably there is oil to be found, but not worth the investment, yet. Don't spread misinformation please. Half of The Chaco was already occupied by Bolivia when the war started. It wasn't Paraguay just starting the war. Same for triple alianza, England had a lot of interest in keeping Paraguay from becoming industrialized.