What sorting method involves breaking data into sets and merging them?

The method that involves breaking data into smaller sets and merging them back together is Merge Sort. This sorting algorithm operates on the principle of divide and conquer. It starts by dividing the array or list into two halves until each subset contains a single element. Although a single element is considered sorted, the algorithm then progressively merges these subsets back together in a sorted manner.

During the merging process, elements from the divided sets are compared and combined into a new sorted sequence. This results in a sorted array or list that is built piece by piece.

Merge Sort is particularly effective for large datasets and is stable, meaning the relative order of equal sort items is preserved. Its average and worst-case time complexity is O(n log n), which makes it more efficient than some other sorting algorithms, especially when dealing with larger datasets. This is why Merge Sort is the correct answer in this context.