united states 和united kingdom前面为什么要加the

英语规定,国家的名字前不加定冠词.但是,如果一个国名的第一个词是由普通名词,也就是,不在国名中的时候,也有意义的时候,必须加the,例如：The great Britain/ THe people's repuiblic...the USA等.不仅如此,其他的地名也是这样：The Great Wall wall 是一个普通名词,在这儿被当作专有名词用.规则很多,要查一查冠词的用法一节如下：
定冠词the的用法
① 表示上文提到过的人或事物.
如：He bought an English-Chinese dictionary this morning.The dictionary is very good.
② 用于单数可数名词前,表示整体或类别.
如：The panda is a rare animal.
此句等于：A panda is a rare animal.= Pandas are rare animals.
③ 用来表示世界上独一无二的事物.
如：the sun,the moon,the sky,the earth,the world
④ 用于表示阶级、党派的名词前.
如：the Chinese * Party,the working class the proletariat 无产阶级
⑤ 常用于含有普通名词或形容词的专有名词前.
A.用于许多江海,山脉,群岛等名词前：
The Yellow River The East Sea the Himalayas the Pacific Ocean
B.用于由普通名词构成的国名：
The People’s * the United States
C.用于机关、团体、朝代、时代、报刊杂志等名词前：
the United Nations the State Council the Tang dynasty the People’s Daily
the Summer Palace the Peace Hotel the British Museum
⑥ 用于表示方位的名词前.
如：the east the southwest the middle the Far East on the left
⑦ 用于乐器名词前,但汉语拼音的乐器前不用冠词.
如：play the piano play the violin play erhu
⑧ 用于复数的姓氏前,表示两夫妇或全家,在此情况下,这类名词作复数对待.
如：When we got there,the Lius were waiting for us.
The Smiths watch TV every day.
⑨ 用于某些形容词或过去分词前,表示一类人或事物.
如：the poor the rich the living the young
the wounded the oppressed the beautiful
⑩ 用在形容词的*前或序数词前.
如：Shanghai is the biggest city in china.
After the game,the first thing they wanted to do was to take a hot bath.