The Yuan emperor Ayurbarwarda maintained friendly relations with Öljaitü, ruler of the Ilkhanate. As for the relations with the Chagatai Khanate, the Yuan forces had, in fact, already for a long time been entrenched in the east. This was originally meant to keep Chapar in submission, but since the latter's defeat in 1310, the garrisons were perceived as a threat to the Chaghadaid state. In order to solve the shortages of pasture grounds, Esen Buqa I, ruler of the Chagatai Khanate sent envoys in an attempt to negotiate with the border garrison commander Tughaji Jinsank in order to convince them to adjust their position in 1312. The negotiations, however, did not go well, and strained relations between the two. Esen Buqa sent tributes to Ayurbarwada in 1312 and 1313, but the Yuan court's attempts to restrict trade between the two states kept tensions high. Ayurbarwada's emissary, Abishqa, to the Ilkhanate while travelling through Central Asia, revealed to a Chaghadayid commander that an alliance between the Yuan and the Ilkhanate had been created, and the allies forces were mobilizing to attack the khanate. Esen Buqa ordered Abishqa to be executed and decided to attack the Yuan because of these events, thus breaking the peace that his father Duwa had brokered with China in 1304. At the same time, Muslim Ozbeg Khan mounted the throne of the Golden Horde in 1312. He proscribed Buddhism and Shamanism among the Mongols in Russia, reversing the spread of the Yuan culture. Yuan envoys seems to have backed Toqta's son, a rival candidate, against Ozbeg. Esen Buqa attempted to gain an alliance of Ozbeg Khan against the Yuan and the Ilkhanate, but without success.
Question: How many years did Esen Buqa send tributes to Ayurbarwada?
Answer: 2