How hard it is to destroy BitCoin system if the government leaders decide to do this? Just wondering, since the government controls the physical internet. The Bitcoin system could be somehow destroyed by the governments.

I'm just wondering if they want to do this, is it technically hard?
since the government controls the physical internet


They do not (at least in North America or Europe). The internet is a network of communication. An Internet Service Provider (ISP) can be private or public, but either way it's function is to direct addressed transmissions to those addresses (IP addresses). 

This network is a kind of base layer. The early days of Bitcoin/crypto found heavy usage in illicit online activities, meaning not allowed by the government. How were these activities carried out in a controlled network? By taking advantage of networks built on top of this base layer internet. TOR, I2P are some examples of these. 

If Bitcoin/crypto were to be heavily prosecuted, nodes could (and have) take refuge in these hidden networks.