I would say that the principal variation in the rapid spread of coronavirus (COVID-19 virus) in countries around the world depends on the generalized employment of the requested preventive measures of the disease in every country. People that have no applied such measures of a generalized form have had a very much bigger and rapid spread of the viral disease. Of course it depends of the exigencies of the respective government and sanitary authorities and the cultural and social level of each country.

According to the way of restrictions and the environmental differences among the places

Different countries had different strategies.

Not well prepared and did not take seriously too.

That's a good question. According to the way of restrictions and the environmental differences between the places.

Countries implemented different strategies to cope with the virus and did so at different points in the Virus' life-cycle. Countries such as Britain imposed their social distancing guidelines later than most European countries such as Britain. Meanwhile, Germany – a major exporter of ventilators and pharmaceutical equipment – was able to research the virus at different stages and contain the spread. This is not the case for a country such as India that imports over 80% of its health care equipment and its health care sector is underinvested in comparison to most advanced economies.