Complex sentence: This breed is very similar to the Sumba or Sandalwood Pony, a breed also developed in these islands, which came from crossing the native ponies on horses of Arabian breeding.
Split into simpler sentences: This breed is very similar to the Sumba pony. They are closely related to the Sandalwood Pony, a breed also developed in these islands, which came from crossing the native ponies on horses of Arabian breeding.