Compare 2 Chronicles 25:5. It will be seen that Uzziah had not added much to the military strength of the nation by his conquests. His army exceeds that of his father Amaziah by 7,500 men only.
Matthew Henry
Concise Bible Commentary
As long as Uzziah sought the Lord, and minded religion, God made him to prosper. Those only prosper whom God makes to prosper; for prosperity is his gift. Many have owned, that as long as they sought the Lord, and kept close to their duty, they prospered; but when they forsook God, every thing went cross. God never continues either to bless the indolent or to withhold his blessing from the diligent. He will never suffer any to seek his face in vain. Uzziah's name was famed throughout all the neighbouring countries. A name with God and good people makes truly honourable. He did not delight in war, nor addict himself to sports, but delighted in husbandry.
SDA Bible Commentary (limited)
Volume 1-7
13. An army. The size of the army, 307,500 men, is comparable to the size of Amaziah’s army of 300,000 men (ch.25:5), but is considerably less than the armies attributed to Asa (ch.14:8) and Jehoshaphat (ch.17:14-18).
With mighty power. If Uzziah was the Azriau of the Assyrian inscriptions, he must have been the dominating figure in Western Asia during the reign of Tiglath-pileser III (745-727). See on 2 Kings 14:28.