Why did the world closed down for the first time for a illness?

"Why did the world closed down"

To allegedly slow the transmission of the virus.

"and my grandpa said that this is another form of the flu which they missed the timing of it"

Many people thought that including the American president and were slow in establishing social distancing, tests etc.

That's why the USA has had nearly 80,000 people die so far, Canada has had 4,629 deaths... bad advice.

Canada succeeded on coronavirus where America failed. Why?

https://www.vox.com/2020/5/4/21242750/coronavirus-...

Because the world is more advanced now. And tell your grandpa covid 19 is much more virulent and contagious and lasts much longer than 'the flu.'

Did grandpa mention that neither SARS nor H1N1 affected the whole world?

I don't suppose your grandpa said anything of the sort. You can always tell a trolls question because they always claim someone else has said something.

If you cant figure out why the world has closed down (as you put it) because of covid 19 now, you never will. Even a 4 year old can figure it out.

Because in the 21st century our science/ technology / knowledge has grown so much that for the 1st time on earth all 8 billion of us can act together to stop and defeat a disease that otherwise would be death for 1/2 of us.

So, the big cost of saving 4 billion humans...shut down normal activity for 1 month or 2.