John Gill Commentary 1 Kings 10:15

"besides [that which] the traders [brought], and the traffic of the merchants, and of all the kings of the mingled people, and of the governors of the country." — 1 Kings 10:15 (ASV)

Besides that he had of the merchantmen, and of the traffic
of the spice merchants
What they paid him as a duty or custom for the importation of their goods:

and of all the kings of Arabia ;
who were subject to him, and paid him a yearly tribute, or at least made presents, see (1 Kings 4:21 1 Kings 4:24)

and of the governors of the country ;
who were viceroys or deputy governors of countries conquered by his father, and who collected tribute from the people, and paid it to him.