If they left later than 1869/70 it wasn't the famine years *per se*.
Starting in the 1860's people in Sweden began MOVING. The first move was usually just to the local market town, but from there they often continued to the cities and also to America.
According to emigrant research the major factors for leaving Sweden were:
* more efficient farming methods (new tools, redistribution of land - laga skifte) which meant that fewer people were needed as farmers
* the rapid increase in population (explained already then by bishop Tegnér as due to the vaccine, the peace, the potatoes) which combined with the fact that fewer were needed to farm meant an enormous surplus of young people with no jobs
* the famine years
* discontent with society (military service, religious intolerance - Swedes did not have full freedom of religion until after WW II !!!!)
Personally I'd like to add another factor: trains and canals. The roads in Sweden were BAD (still are!) and trains caught on very quickly once they were introduced in the 1850's. Going by boat was another preferred way of travelling. Without these new modes of transport the great migration would probably not have reached the numbers it did.
The reasons for going to America (as opposed to staying in a Swedish city or moving to e.g. Australia) were:
* the (seemingly inexhaustible) supply of fertile land and work
* emigration propaganda
* the emigrants' letters home to Sweden (in the letters they had *all* succeeded)
I'd like to add: the ready availability and affordability of tickets to America. They were sold EVERYWHERE, 17 (!!) shipping lines had agents all over Sweden, tickets could be bought not only in towns but in small villages right across Sweden.
The years 1879-1893 were the busiest years of emigration and during these 15 years a total of 485.000 Swedes emigrated. During the top five years more than 40.000 people emigrated every year. A normal Swedish town TODAY has about 30.000 inhabitants - so this was mass hysteria!
It may be impossible to find out exactly WHICH of these factors influenced your ancestors the MOST. As with most people it was probably a mix. They may not even have been very sure themselves. Also, we tend to think that people left for good but as a matter of fact 200.000 (out of 1.3 million) returned, permanently (my grandmother was one of them), and huge numbers went back and forth over the Atlantic several times! This of course made it easier to move, the decision wasn't irrevocable.
/Ingela