I am in the same boat. My grandfather was born in 1889 in Fondochello, Sicily, served in the Army sometime before immigrating to the US in 1912

I am looking for military information on my grandfather, Joseph Grasso, born 1889 in Fondochelli, Sicily. I have a painting of him in his Italian Army uniform that hung on my grandmother’s wall, I took it when she died. Where would I start? Thanks