Complex sentence: De jure recognition is of course stronger, while de facto recognition is more tentative and more connected with effective control of the recognised state over its territory, as when the United Kingdom recognised the Soviet Union de facto in 1921, but de jure only in 1924.
Split into simpler sentences: De jure recognition is stronger, while de facto recognition is more tentative and relates more to recognizing that a government exercises control over a territory. An example of the difference is when the United Kingdom recognised the Soviet Union de facto in 1921, but de jure only in 1924.