K-cores analysis of co-country matrix (red nodes, k=19; pink nodes, k=18; purple nodes, k=17; yellow nodes, k=16; deep blue nodes, k=15; earthy yellow nodes, k=14; ice blue nodes, k=13; brown nodes, k=12; blackish green, k=11; green nodes, k=9; gray nodes, k=7; sky blue nodes, k=6; modena nodes, k=5; black nodes, k=1)