Complex sentence: The economy of Sunda kingdom relied on agriculture, especially rice cultivation; this is reflected in Sundanese culture and the annual ceremonies of crop seeding and "Seren Taun" rice harvest festival.
Split into simpler sentences: The economy of Sunda kingdom rely highly on agriculture, especially rice cultivation. It is clearly reflected in Sundanese culture and annual cycle of activity which incorporated ceremony of crop seeding and "Seren Taun" rice harvest festival.