Hi, I'm Swedish and not an expert on danish history but I'll give your question a shot. Lots of people migrated from Europe to the US during the 19th and early 20th centrury, I've seen the number 50 million mentioned. Why did all these people leave Europe? Some left due to religious persecution, but the main driver of the migration was poverty and the hope of better life conditions, sometimes coupled with a sense of adventurism. Similar to much to the migration that we still see today.

Improved living conditions during the 1800:s saw a rapid population growth throughout Europe. This was of course a positive, but it created a dilemma for farmers. As more and more children survived, the sibling would have to share increasingly smaller plots of land inherited from their parents. By the end of the 19th century, 27 % of Danish farmers had landholding of less than 1,2 acres. This was insufficient to support a family, and thus many children of farmers gave up farming and began migrating within the country, from rural areas into the cities.

However, while Denmark industrialized faster than its Nordic neighbors, the cities couldn't provide opportunities for everyone. With the large numbers of laborers around, some couldn't find work and the ones that did worked for low wages. On top of that, while serfdom had been abolished in Denmark, rural laborers where denied many rights that applied to urban laborers and could among other things be subject to corporeal punishment from their employer. Being a worker from a rural area in a danish city was thus a hard life, if indeed you managed to find work at all. And even if you where an urban worker, that excess work force availability affected your salaries too. This in turn would create incentives for many people to look for better opportunities elsewhere.

The detail about your great grandfather first going to Sundsvall is interesting to me, obviously that's in the opposite direction, so we might assume that his plan wasn't to go to America when he went there. Coming from that area, I know there where large logging and iron mill industries in that area during the time, perhaps he went to Sundsvall to find employment in one of those fields?

You did mention that his father was making a good living however, so why would all the brothers leave? This becomes speculation, but certainly many young men left for America not just due to poverty but also based on a sense of adventure, similarly to why many young people might move cities or countries today. This was also during a period of "manifest destiny" in the US, which created incentives for European immigrants that wanted to colonize the west. The fact that large scale emigration to America had been ongoing for over 20 years when your relatives left would also have made it easier for them both mentally and logistically as they might have been able to find information about life in America from newspapers or friends who had left before them, and with well established routes to take them there, and fare prices that had gradually been lowered throughout the 1880s.

Sources:

Mass Emigration from Denmark to the United States 1868-1914

The Pursuit of Power - Europe 1815 - 1914. Richard J. Evans.

On both sides, my parents’ ancestors came to Utah in the late 1800’s, most from Sweden and Denmark. Many in Utah are still very ethnically Scandinavian, in surname and appearance.

I’ve read that about 30k or so Scandinavian immigrants came to Utah, most after the transcontinental railroad was completed in 1869, making the overland journey less arduous and more affordable.

It’s difficult to know exactly why they left however. Most seemed to be pushed by economic factors at home and pulled to the US by opportunity and the lure of the new.

I’m no longer practicing LDS (aka Mormon) and tend to question official church accounts that emphasize religious motivations, although I’m sure that played a part. As in the official state Lutheran church had perhaps failed to meet the needs of ordinary people.

Here’s one of many papers written on the subject of Utah immigration:

https://amp.issuu.com/utah10/docs/volume_23_1955/s/95100

Continued

The Seattle national Nordic museum is another great resource for understanding Scandinavian heritage and immigration. They explain many of the economic impulses leading to immigration to the USA. But interestingly seem to be oblivious to the LDS factor…

If you’re in the PNW and interested in Nordic culture, do check it out.

https://nordicmuseum.org

You mention that your Danish ancestor entered Canada rather than the US at that time. I’d like to give a little more context about draws to Canada at that time. From 1870-1930, thanks to the Dominion Land Policy, European folks willing to become farmers could come to Canada and be given a land grant of arable land simply for the promise to farm and develop it. A lot of that granted land was in the prairies, which is still Canada’s bread basket, and is some of the best grain-growing farmland in the world. Several brothers looking to make their start in life, who’ve heard about this offer overseas for land, which has now had 20 years of traction to prove its validity with returning folks telling their tales and propaganda posters painting Canada and America as golden lands of opportunities? An adventurous gamble for the bravehearted youths?

There’s some more interesting reading about prairie settlement, and specific measurements of land grants here: https://www.thecanadianencyclopedia.ca/en/article/dominion-lands-policy

Something else you mention is multiple brothers—several generations of multiple brothers could lead to Danish family property being split, and split again in subsequent generations, making it progressively harder to earn a living with the same land/business. Unless of course there was Danish law at the time akin to British law which prevented the division of property/lands/estates and thus forced property inheritance generally to go to one male heir, with cash inheritance and/or separate properties going to other heirs. I am not an expert in this law area, but would be curious to learn more! Either way, there would not be enough family property to go around and all of the brothers except for one would need to figure out some way of their own to make it in the world.

Quite frankly OP, I’m surprised that none of the 1870s ancestral family members stayed behind in the family home, if it was owned by the family at that time. I’d be curious as to who lives there now, and that family’s story!

Have you looked at the church books for that location in Denmark?

Denmark isn't an area I normally research, but it should have birth/marriages/deaths, and could have a section for people moving to/from a parish.

You can also look for any census records.

In cases of an individual, a bigger picture often can be found by looking at those around them. That includes kin and neighbors. Both from where the were from and where they went to. For example, in my research, I found no reason why a certain individual left, but researching emigration from their village turns up a rather good reason why so many people left around that time.

Also, in the US, if they ended up in a small town, there can be a rather intrusive level of detail about people recorded. Old newspapers can be full of gossip like who is visiting who or who is ill.

FamilySearch tends to have a good overview, but it is affiliated with the Latter Day Saints. Here's (their page on Danish church records)[https://www.familysearch.org/en/wiki/Denmark_Church_Records].

Note that if you do go down the genealogy route, most online family trees have questionable accuracy.