This was a time of great affluence for the Siamese Nation and its Capital City was referred to as "Golden Ayutthaya". Contact and trade with neighbouring nations, such as Malay Sultans and, especially, Japan plus the growth of European trading and diplomatic missions brought wealth to Ayutthaya as never before. However, such exposure also brought the risk of unwanted influences in particular from the empire building European countries. King Narai often walked the tightrope of dilemma in balancing pressures from Europe against, more importantly, the protection of his Kingdom of Ayutthaya, his Nobility and Thai subjects.
It was not long into King Narai's reign when, in 1660, Chinese forces invaded and captured the Burmese Kingdom of Ava. Conscious that this could upset the delicate balance of regional power in his northern vassal states, King Narai worried about his northern provinces especially Chiangmai because he wasn't convinced he could trust the ruler of that Lanna Thai kingdom. The King marched north taking Lampang and many of the smaller towns in the Chiangmai region, however, his force was not strong enough to attack Chiangmai and he returned to Ayutthaya in 1661.
Soon after, King Narai marched again on Chiangmai and, aided by his competent military commander Chao Phya Kosathibordi, quelled Chiangmai and brought the city back under his direct influence. During his time in Chiangmai, King Narai married the daughter of the ruler of the city and, later, they had a son Prince Laung Sorasak (who eventually will become Siam's infamous "Tiger King"). With his northern problem taken care of, King Narai was free to address the matter of foreign relationships.
In the interests of peace, they got their monopoly and also, in 1664 , the signing of a treaty between Ayutthaya and the Netherlands. Perhaps the Dutch were upset at just having lost their settlement of New Amsterdam to the British (who promptly renamed it "New York") because The Dutch East India Company's imperialist style may be noted from one proviso in the treaty which read "In case (God forbid) any of the company's servants shall commit a serious crime in Siam, the King and the judges shall not have the right to judge him, but he must be handed over to the company's Chief, to be punished according to the Netherlands' Law".
It should be mentioned that in 1678 a certain Greek cabin boy, aboard one of the English East India Company vessels, arrived in Siam. He was Constantine Phaulcon and he rose to great importance in the Royal Court of Ayutthaya. Accordingly, when the French emissaries arrived, accompanied by the Jesuit missionaries, Constantine Phaulcon was there to assist and interpret for them.
King Narai welcomed the French ambassadors and, likewise, the Jesuits because among their number were men of skills and mathematics. Men like Father Thomas who, aside from missionary intentions, was also an engineer and architect. In fact, Father Thomas assisted King Narai in construction projects at Ayutthaya, Bangkok and Thonburi. The King trusted these missionaries and gave them land on which to build their own homes and sacred places. A hidden agenda was never thought of.
King Narai, The Great died from dropsy the following year in 1688. He further opened his Kingdom to trade, commerce and diplomacy Golden Ayutthaya blossomed. But he also took risks in permitting Europeans to have too great an influence at his Royal Court. Despite those European pressures, the Kingdom of Ayutthaya survived intact and foreign influence was brought under control.