《汉书·传·匈奴传上》
这时，昭帝死了，汉宣帝继位，乌孙国首领昆弥又上书汉天子，说： 我们接连被匈奴侵伐削弱，我愿意把国中一半的精兵共有五万人马都拿出来，尽全力反击匈奴，希望汉天子派兵，救救公主！ 
昭帝崩，宣帝即位，乌孙昆弥复上书言： 连为匈奴所侵削，昆弥愿发国半精兵人马五万匹，尽力击匈奴，唯天子出兵，哀救公主！ 
At this time, Emperor Zhaodi died and Emperor Xuandi of the Han succeeded to the throne. The leader of Wusun Kunmi wrote to the emperor of the Han Dynasty again, saying: We have been repeatedly invaded and weakened by the Xiongnu, I am willing to take out half of the elite soldiers in the country, a total of 50,000 troops, to fight back against the Xiongnu with all my might. I hope the emperor of the Han Dynasty will send troops to rescue the princess!
<s>[INST] Kindly elucidate the central themes in this passage in English: 昭帝崩，宣帝即位，乌孙昆弥复上书言： 连为匈奴所侵削，昆弥愿发国半精兵人马五万匹，尽力击匈奴，唯天子出兵，哀救公主！  [/INST] At this time, Emperor Zhaodi died and Emperor Xuandi of the Han succeeded to the throne. The leader of Wusun Kunmi wrote to the emperor of the Han Dynasty again, saying: We have been repeatedly invaded and weakened by the Xiongnu, I am willing to take out half of the elite soldiers in the country, a total of 50,000 troops, to fight back against the Xiongnu with all my might. I hope the emperor of the Han Dynasty will send troops to rescue the princess!</s>
Kindly elucidate the central themes in this passage in English: 昭帝崩，宣帝即位，乌孙昆弥复上书言： 连为匈奴所侵削，昆弥愿发国半精兵人马五万匹，尽力击匈奴，唯天子出兵，哀救公主！
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At this time, Emperor Zhaodi died and Emperor Xuandi of the Han succeeded to the throne. The leader of Wusun Kunmi wrote to the emperor of the Han Dynasty again, saying: We have been repeatedly invaded and weakened by the Xiongnu, I am willing to take out half of the elite soldiers in the country, a total of 50,000 troops, to fight back against the Xiongnu with all my might. I hope the emperor of the Han Dynasty will send troops to rescue the princess!
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