Complex sentence: On 3 September, the UK and France declared war on Germany as obliged by the Anglo-Polish military alliance, the declaration was made 24 hours after the UK had issued an ultimatum to Germany to withdraw all German forces from Poland.
Split into simpler sentences: On 3 September, the UK and France declared war on Germany as obliged by the Anglo-Polish military alliance. The declaration was made 24 hours after the UK had issued an ultimatum to Germany to withdraw all German forces from Poland.