Task: Question Generation
Input (English): Passage: Although it failed to dislodge the Burmese from Kengtung and Sipsongpanna at the beginning of the century , Siam never gave up its claims on these lands. They tested the waters in 1849, by raiding as far north as Kengtung. But when the Second Anglo-Burmese War started, the Siamese viewed it as their opportunity to take over the trans-Salween states. In late 1852, a large infantry and elephant force marched from Chiang Mai and launched a two-pronged invasion of Kengtung. Burma couldrespond only after the new king Mindon had seized power in February 1853. Because he was still concerned about the British threat, Mindon could only send several thousand infantry troops from the Mone  garrison to relieve the Siamese siege of Kengtung. With the troops by Kenghung sawbwa, the Burmese eventually drove out the Siamese but only after heavy loss of life. In 1854, the largest Siamese invasion force, consisted of Laotian levies, tried once more. But this time, with the British front quiet, the Burmese were ready. Mindon had deployed a larger, well-equipped army . The Siamese forces again reached Kengtung but could not break through. The Siamese forces withdrew to the border in May 1855.
Output (English): How many years did the Siamese forces fight before withdrawing to the border in May 1855?