What does Daniel 5:30 mean?

The night Daniel interpreted the handwriting on the wall (Daniel 5:1–5) was the very night Belshazzar drew his last breath. In the strictest sense, we are not sure exactly what happened to Belshazzar. The only two details we're given are that he died and this occurred the very same night. Likewise, the following verse might well have skipped over political events to reach the background of Daniel's next story (Daniel 6:1–3).

At one time, a Persian siege cleverly got around Babylon's defenses by diverting a river and entering under a sluice gate. That might have occurred when Belshazzar was minding the city on behalf of Nabonidus, his father, who was away at the time. It's also possible the king died that night from some other cause—the point of the story is not so much "how" the prophecy was fulfilled as the fact that it came true.

In the historical event regarding the river, the Persian army invaded through the wall's river openings and the city surrendered without a fight. Historians date Babylon's fall as the 16th of Tishri, or October 12, 539 BC. Isaiah 13:20, 47:1–5, and Jeremiah 51:43 prophesy a complete devastation of Babylon, but that did not happen when the Persians conquered Babylon. This prophesied event awaits the tribulation. The final overthrow of Babylon and her corrupt allies is previewed in Psalm 2:4–6 and fulfilled in Revelation 19:15–16, when Jesus returns to earth.