The beginning of Newt Scamander's story includes him arriving on America's shore by boat. My understanding from the Harry Potter world is that long-distance travel can be accomplished by portkey, regardless of if the travellers has been there before or not. The portkey can also be used by those who still have the Trace on them, and also doesn't require knowledge of powerful travelling spells, such as apparating and disapparating.
A wizard may choose to travel via apparition, even across continents I believe (please correct me if I'm wrong), however Newt still chose to travel via boat. Rather, again, even by Floo. I don't have a full record of the Floo network and if this is also cross-continental, however I would wonder why America is so off-limits to the magical community. At least, I don't think many wizards would find rubbing shoulders with muggles/no-majes very fun, less-so for such a long duration trip. Any extended method of travel, perhaps by hopping to islands of portkeys, traversing their dot-to-dot trip in stages as per the maximum distance travellable.
Is there any reasonable evidence to suggest the Americas are kept distant from the English wizarding community, or perhaps any evidence to suggest that the Floo network doesn't extend to America, or even that Portkeys are insufficient for such long-distance travel?