This is the full paragraph and context of the first sentence you've included:
Vijayanagar, the capital of one of the largest Hindu empires ever, was founded by Sangama dynasty princes Harihara and Bukka in 1336. Its power peaked under Krishnadevaraya (1509-29), when it controlled nearly the whole of the peninsula south of the Krishna and Tungabhadra rivers. Comparable to Delhi in the 14th century, the city, with an estimated population of half a million, covered 33 sq km and was surrounded by several concentric lines of fortification. Its wealth derived from the control of spice trade and the cotton industry. Its busy bazaars, described by travelers such as Portuguese Nunez and Paes, were centers of international commerce. The empire collapsed after the battle of Talikota in 1565 when the city was ransacked by a coalition of Deccan sultans (Bidar, Bijapur, Golconda, Ahmednagar).
In the above passage, the reason for use of the phrasing -- 'its wealth derived from' -- is because the passage refers to something in the historical past. 'Its wealth had been derived from' or 'its wealth was derived from' would also be grammatically correct substitutions you could use here if you were drafting your own sentence.
However, just saying -- its wealth derived from -- in the proper context can also be used in reference to the present tense as well. The main reason that 'is' wasn't used in the above passage is that the Vijayanagara Empire no longer exists. However, you can also use the phrase -- its wealth had been derived from -- and refer to something existing in the present tense as well; you just need further clarification in the sentence itself.
For example, you could say the following: Its wealth derived from the petroleum industry, Saudi Arabia is just now letting women begin to drive.