There were 900 people a week landing in NY every week alone.
As said before: The virus entered Italy early December. Some 10'000 Chinese working slaves were allowed to visit their families over new year and did in January directly return from Wuhan region. The surge in Italy was after the Chinese new year return of the "slaves". ("slaves" because these people are hired under Chinese law ...)
Italy did finally spread it to USA and south Switzerland. Thus first stop here was the travel to south Switzerland!
In Germany the situation was the same. A automobile contractor working with BMW sent people from Wuhan to Munich that did spread the first mass infection that almost could be contained. But as we know there are asymptomatic super super spreaders you never will catch early...
As reported form the German meet industry: Super spreading happened over distances > 8 meter of the individual! Due to low air temperature and ventilation!