Complex sentence: On 17 April 1941, Yugoslavia was occupied by Nazi Germany and was reorganised into four provinces under foreign rule; a royal government-in-exile, recognized by the United Kingdom and later by all the Allied powers, was established in London.
Split into simpler sentences: On 17 April 1941, the Kingdom was invaded and occupied by Nazi Germany and organised into four provinces under foreign rule. A royal government-in-exile, recognized by the United Kingdom and, later, by all the Allied powers, was established in London.