Despite Egypt's size and wealth, Assyria had a greater supply of timber, while Egypt had a chronic shortage, allowing Assyria to produce more charcoal needed for iron-smelting and thus giving Assyria a greater supply of iron weaponry.
This disparity became critical during the Assyrian invasion of Egypt in 670 BC.
Firstly there is a dispute about the utility of a very artificial term that covers an extremely long and complicated period of Egyptian history.
The Third Intermediate period includes long periods of stability as well as chronic instability and civil conflict: its very name rather clouds this fact.
He proceeded to found the Upper Egyptian Libyan Twenty-Third Dynasty of Osorkon III – Takelot III – Rudamun, but this kingdom quickly fragmented after Rudamun's death with the rise of local city states under kings such as Peftjaubast of Herakleopolis, Nimlot of Hermopolis, and Ini at Thebes.
The Nubian kingdom to the south took full advantage of this division and political instability.
Consequently, Pharaoh Taharqa's reign, and that of his successor and cousin Tantamani, were filled with constant conflict with the Assyrians.
Pharaohs, such as Taharqa, built or restored temples and monuments throughout the Nile valley, including at Memphis, Karnak, Kawa, Jebel Barkal, etc.
In Thebes, a civil war engulfed the city between the forces of Pedubast I, who had proclaimed himself Pharaoh versus the existing line of Takelot II/Osorkon B.
These two factions squabbled consistently and the conflict was only resolved in Year 39 of Shoshenq III when Osorkon B comprehensively defeated his enemies.
Pharaoh Psamtik III had succeeded his father Ahmose II for only 6 months before he had to face the Persian Empire at Pelusium.
The Persians had already taken Babylon and Egypt was no match.
The period was one of decline and political instability, coinciding with the Late Bronze Age collapse of civilizations in the Near East and Eastern Mediterranean (including the Greek Dark Ages).