During the civil war, the union benefitted from a steady stream of new immigrants, some of whom fought in the war. what kept the south from enjoying the same measure of ?

The south did not have a large influx of immigrants because it had a weak economy, based on rural labor with slaveholding latifundium.

Explanation:

In the north, capital accumulated during the colonial period created favorable conditions for industrial development whose labor and market were in wage labor. The abundance of hydropower, mineral wealth and ease of transportation contributed greatly to a large influx of immigrants and to the progress of the region, which advocated a protectionist economic policy. The south, with a hot and dry climate, remained behind with an agro-exporting economy of cotton and tobacco, based on slaveholding latifundium. Industrially dependent, the south was frank defender of the free-trade, characterizing more a counterpoint with the reality of the north.