This post is intended for SharePoint Online and 2016+ using CSOM.

In previous version of SharePoint, moving a folder structure to a different library or a different library in another site collection required a good amount of code and effort. With the introduction of Microsoft.SharePoint.Client.MoveCopyUtil we now have the ability to use methods like MoveFolder to perform a cut and paste of a folder structure. There are other methods that are worth exploring like FolderCopy that is a copy and paste of a structure.

More methods can be found here: MoveCopyUtil members

	Name	Description
	CopyFile
	CopyFileByPath
	CopyFolder
	CopyFolderByPath
	MoveFile
	MoveFileByPath
	MoveFolder
	MoveFolderByPath

Example of moving a folder between site collections.

string dstUrl = "https://sharepoint.com/sites/B/";

using (ClientContext srcContext = new ClientContext(dstUrl))
{
  string sourceFolder = "https://sharepoint.com/sites/A/libraryname/foldername";
  string destFolder = dstUrl + "libraryname/foldername";

  MoveCopyUtil.MoveFolder(srcContext, sourceFolder, destFolder);
  srcContext.ExecuteQuery();
}

Again, this is using CSOM with the latest version of the NuGet package (16.0.4351.1000).