The Kingdom of Cambodia is centered at the Mekong, prospering as an integral part of the Asian maritime trade network,^[69] via which the first contact with European explorers and adventurers does occur.^[70] By the 17th century Siam and Vietnam increasingly fought over control of the fertile Mekong basin, enhancing pressure on weakened Cambodia. This marks the beginning of direct relations between post-Angkor Cambodia and Vietnam. The Vietnamese on their "Southward March" reach Prei Nokor/Saigon at the Mekong Delta in the 17th century. This event initiates the slow process of Cambodia losing access to the seas and independent marine trade.^[71]