Well, what you have to remember is that China was crushed and divided by conquerors for more than a century. The Qing dynasty saw the opium wars and made a lot of Chinese very distrustful of westerners. The Democracy set up by Sun Yat-sen, saw a corrupt democracy (Thanks to Chang Kai-Shek) and a lot of Communists had a distrust of some democracies.

Now, this isn't to say that they were totally closed off. The USSR was a big ally, in the beginning. The USSR and the Maoist regime had a falling out over ideology, and which direction to take communist. Mao thought differently of Leninist Communism. Good explanation of Maoist "Superiority" can be found here.

One example of this Maoist thought, was the belief that the First and Second World countries were still imperial nations, who continued to exploit the third world countries. Thus there couldn't be any real Communists in their, as the proletariat were located in the third world. This kind of thinking damaged relations in the west.

China however, wasn't against opening up its borders to some third world countries near its borders. It mainly saw took the time in this era to try and export Maoist ideology to other countries, especially from '65-'68 during the Cultural Revolution. (Aside from Pakistan, who was probably one of their biggest allies, and still is today.) Thanks to being exiled by the USA, since the PRC wasn't internationally recognized as the proper government of China, a lot of countries didn't want to open up their borders to them, as well.

Basically until Deng Xiaoping took control, and re-thought a lot of their economic policies, they didn't open up to much to democratic thought..

(I'll be back later in an edit with better sources, for more detailed readings)

It goes back further - for years during the Qing dynasty and before were isolationists as well