Complex sentence: ISIL said that the attacks were carried out in retaliation to the 2015 Egyptian military intervention in Libya, Egyptian military action (air and ground) following kidnapping and beheading of 21 Copts in Libya in February 2015.
Split into simpler sentences: ISIL said that the attacks were carried out in retaliation to the 2015 Egyptian military intervention in Libya. Egyptian forces had waged military air and ground action following kidnapping and beheading of 21 Copts in Libya in February 2015.