Question: Who conquered the babylonian empire in 539 bc?

Disambiguated questions and answers:
context: The Fall of Babylon denotes the end of the Neo-Babylonian Empire after it was conquered by the Achaemenid Empire in 539 BCE. 
question: Which empire conquered the babylonian empire in 539 bc?
short_answers: Achaemenid Empire

Persian

First Persian Empire

Achaemenid
wikipage: Fall of Babylon

context: It was in the sixth year of Nabonidus (550/549 BC) that Cyrus the Great, the Achaemenid Persian king of Anshan in Elam, revolted against his suzerain Astyages, king of the Manda or Medes, at Ecbatana. Astyages' army betrayed him to his enemy, and Cyrus established himself at Ecbatana, thus putting an end to the massive Median Empire and making the Persian faction dominant among the Iranic peoples. Three years later Cyrus had become king of all Persia, and was engaged in a campaign to put down a revolt among the Assyrians. Meanwhile, Nabonidus had established a camp in the desert of his colony of Arabia, near the southern frontier of his kingdom, leaving his son Belshazzar ("Belsharutsur") in command of the army.
question: Which ruler conquered the babylonian empire in 539 bc?
short_answers: Cyrus II of Persia

Cyrus the Elder

Cyrus the Great
wikipage: Fall of Babylon

context: In another reconstructed account, Nabonidus sent his son Belshazzar to head off the huge Persian army, however, already massively outnumbered. Belshazzar was betrayed by Gobryas, Governor of Assyria, who switched his forces over to the Persian side. The Babylonian forces were overwhelmed at the battle of Opis. Nabonidus fled to Borsippa, and on 12 October, after Cyrus' engineers had diverted the waters of the Euphrates, "the soldiers of Cyrus entered Babylon without fighting." In Xenophon Belshazzar is reported to have been killed, but his account is not held to be reliable here. Nabonidus surrendered and was deported. Gutian guards were placed at the gates of the great temple of Bel, where the services continued without interruption. Cyrus did not arrive until 3 October, with Gobryas having acted for him in his absence. Gobryas was now made governor of the province of Babylon.
question: Which army conquered the babylonian empire in 539 bc?
short_answers: Persian army

soldiers of Cyrus

Achaemenid
wikipage: Fall of Babylon

Long answers:
knowledge: content: The Neo-Babylonian Empire, also known as the Second Babylonian Empire[5] and historically known as the Chaldean Empire,[6] was the last of the Mesopotamian empires to be ruled by monarchs native to Mesopotamia.[7] Beginning with Nabopolassar's coronation as King of Babylon in 626 BC and being firmly established through the fall of the Neo-Assyrian Empire in 612 BC, the Neo-Babylonian Empire and its ruling Chaldean dynasty would be short-lived, being conquered after less than a century by the Persian Achaemenid Empire in 539 BC.
wikipage: Neo-Babylonian Empire
long_answer: The Neo-Babylonian Empire, also known as the Second Babylonian Empire,  was the last of the Mesopotamian empires to be ruled by monarchs native to Mesopotamia. The Neo-Babylonian Empire and its ruling Chaldean dynasty would be short-lived, being conquered after less than a century by the Persian Achaemenid Empire in 539 BC. Cyrus the Great, the Achaemenid king of Persia, used his Persian army to overwhelm the Babylonian forces.