I know----TL;DR
Bessemer Process replaced crucible steel making in the late 1800s reducing costs and making it possible to produce much larger quantities and ability to produce/roll flat steel(improved economies of scale). Basic Oxygen Process replaced Bessemer around WW2 enabling much better chemistry control and much better shape control (think hood stock/fender stock for automobiles).
All steel made by BOF required access to high quality iron ore, including even the lowest quality items (think cast iron/heavy plate/beams/channels/angles) so steel making pretty much restricted to physical areas where iron ore can be brought in by water transport or is a readily available resource.

Circa 1960-----
Cost for building BOF processing = approximately $1000/ton of capacity
Manufacturing costs of BOF = approximately $1100/ton

1960s - introduction of Electric Arc steel making.
Downside - only can use to produce shapes - no flat so BOF still required to make flat steel. By this time flat steel now makes up 75% of demand in the US (building "boom" for east coast for beams/channels etc...is over. High use areas now automotive, appliance, and metal building). Nucor with EA Furnaces takes complete and total control of all shape markets except specialty bar products that require special chemistry only available thru BOF.

1980s - introduction of Electric Arc flat steel made from DRI (direct reduced iron) and scrap. High quality painted surfaces still require chemistry and shape that can only be controlled thru BOF but all other flat requirement are now turned into commodity products that can be made any where at a cost structure of about 1/3 of BOF.
EAF estimated at $400/ton to build and $300/ ton to manufacture (not near as many man hours per ton required - all done systemically).
2010s - Not yet widely known - rolling processes perfected by Germans and Japanese enable chemical and shape control in Electric Arc Furnaces to allow for critical items to be produced. Only equipment available for this now in the US at Big River Steel. Steel Dynamics - Columbus MS only one step behind.
Point is - until 1990s BOF production (with 80% of US capacity between Chicago and Buffalo) was competing with imports on the southern and west coasts----and they didn't care because 75% of demand was in the same Chicago to Buffalo corridor. interior transportation costs killed import competitiveness there.
In the 1990s imports began making inroads into the mid-west with lower cost (labor), subsidized product from socialist/communist countries made with old equipment from closed US mills (cheap purchase price of assets). Only way for US producers to compete was lower price or new Electric equipment. Market downturn forced all but a couple into bankruptcy. Even sadder news is that most of those old mills with high labor costs are still in operation and will be replaced by much less expensive to operate electric furnaces in the next 10 to 25 years. It's gonna happen again.