Complex sentence: In 1999 a city-sized alien spacecraft crashes in South Ataria Island on Earth and over the course of 10 years a military organization called the "U.N. Spacy" reverse-engineers the technology and rebuilds the spacecraft calling it the SDF-1 Macross.
Split into simpler sentences: In 1999 a city-sized alien spacecraft crashes in South Ataria Island on Earth. Over the course of 10 years the military organization "U.N. Spacy" reverse-engineers the technology and rebuilds the spacecraft, naming it the SDF-1 Macross.