Allied means joined together for a common purpose, especially in cooperation or partnership. When groups become allied, they work as teammates rather than competitors or strangers, combining their strengths to achieve something neither could accomplish alone.

The word comes up most often in history and politics. During World War II, countries like the United States, Britain, and the Soviet Union became allied against Germany, Italy, and Japan. These countries were called the Allies, working together despite their differences because they shared a crucial goal. Before the war, some of these nations had been rivals or even enemies, but the threat they faced was so serious that they formed an alliance.

You'll also see allied used more broadly. Two students might become allied in their campaign to improve school lunches, or neighboring towns might form allied fire departments that help each other during emergencies. Scientists from different universities often work as allied researchers on complicated problems.

The word suggests something stronger than just cooperation: it implies a formal or serious partnership where each side can count on the other. Allied groups don't just happen to work together occasionally; they’ve made a commitment to support each other toward their shared goal.