During thr 16th century the power of Cambodia was beginning to decline. The Siamese military emerged and attack the Khmer Empire. The Siamese attack and defeats the Khmer king. The Empire began to lose control after the Thais captured the capital.
Then, during the 18th century, Cambodia was found between two powerful countries, Thailand and Vietnam. The Thais kept invading Cambodia in the 18th century. Eventually, they destroyed Phnom Phen.