After three years, King Nebuchadnezzar tested the trainees. In all wisdom and understanding, the four were ten times better than the wise men in his court. Even while exiled in a foreign country, God put these four in place as Nebuchadnezzar's advisors to protect the Jews while in Babylon.

Now at the end of the days that the king had said he should bring them in, then the prince of the eunuchs brought them in before Nebuchadnezzar. And the king communed with them; and among them was found none like Daniel, Hananiah, Mishael, and Azariah: therefore stood they before the king. And in all matters of wisdom and understanding, that the king enquired of them, he found them ten times better than all the magicians and astrologers that were in all his realm (Daniel 1:18-19, 20).

References: 21st Century Revelation: World Wars, Iraq Wars & End Wars - Chapter 13 - Minor Feasts, Major Events, Chapter 14: Israel's Time Out, Chronology of Man

Under the Mosaic Law, Israel was required to be faithful or they would go back into captivity. After Egypt, the children of Israel rebelled against God and they wander in the desert forty years (Numbers 14:34). During the judges, Israel was persecuted by their Canaanite neighbors for their incomplete obedience (Joshua 23:13). During the kings of Israel and Judah, they returned to idols. In 721 BC, Israel fell to Assyria (2 Kings 17:6-7) and in 712 BC, Assyria fell to Babylon (Iraq). Despite the prophets' warnings, Judah was repeatedly attacked by Babylon in 605, 597, 586 and 582 BC. Jerusalem and the Jewish temple were destroyed on the 9th of Av, 586 BC. Even with seventy years of captivity, God had a plan for His people Israel through Daniel (Jeremiah 25:11-12).

Them that had escaped from the sword he [Nebuchadnezzar] carried away to Babylon; where they were servants to him and his sons until the reign of the kingdom of Persia: To fulfil the word of the Lord by the mouth of Jeremiah, until the land had enjoyed her sabbaths: for as long as she lay desolate she kept sabbath, to fulfil seventy years (2 Chronicles 36:20-21).

As God used Israel to judge the Canaanites, He used Babylon to judge Judah. In 605 BC which was the third year of Jehoiakim, Nebuchadnezzar of Babylon attacked Jerusalem and captured Jehoiakim. He took some of the vessels from the Jewish temple and put them in the temple of the Babylonian god. He deported some of the nobility of Israel that were educated and wise to advise the king and to learn the ways of the Babylonians. Those selected were Daniel (Belteshazzar), Hananiah (Shadrach), Mishael (Meshach) and Azariah (Abednego). They were trained three years before serving as the king's personal advisors and wise men.

… he should bring certain of the children of Israel, and of the king's seed, and of the princes; Children in whom was no blemish, but well favored, and skillful in all wisdom, and cunning in knowledge, and understanding science, and such as had ability in them to stand in the king's palace, and whom they might teach the learning and the tongue of the Chaldeans (Daniel 1:3, 4).

Since training for the king's court, the group was given the king's food and wine. Even though Daniel was in a foreign land, the dietary rules of the Law still apply. So Daniel purposed in his heart not to defile himself which directly affected others. He asked Ashpenaz that instead of eating the king's food, the Jews would eat vegetables and water. Ashpeaz was fearful of the consequences so Daniel asked to test them ten days. Afterward, Melzar compared the four with those that ate the king's meat. Because they were healthier, he decided that the whole group should follow Daniel's diet. God gave the four men special favor in knowledge, learning and wisdom and Daniel could interpret dreams and visions.

The king appointed them a daily provision of the king's meat, and of the wine which he drank: so nourishing them three years, that at the end thereof they might stand before the king. But Daniel purposed in his heart that he would not defile himself with the portion of the king's meat, nor with the wine which he drank. As for these four children, God gave them knowledge and skill in all learning and wisdom: and Daniel had understanding in all visions and dreams. (Daniel 1:5, 8, 17).