Not having strict adherence to polices firmly dedicated to totally eradicating all aspects of confederate influences across the board, resulted in severe problems extending from the mid/late 1860's to the mid 1960's, effecting the entire nation adversely in a number of respects, plus being an embarrassment overseas, resulting in reluctance to corporately invest in such a culture's stubborn backwardness & adverse working environment until the old ways were forced to the back woods.
Governmental positions should have been filled with as many known, qualified, pro-Union Southerners as possible. A national campaign similar to post war Europe, specifically Germany's example of a major Allied effort to root out as many previous problems & future potentials from the period of 1933-1945 could not be totally enacted resulting from Russia's communist threats of expansion rapidly becoming paramount to all other concerns on the Continent.
Rigorous enforcement of existing Reconstruction policies were not handled properly in some areas. Allowing, in many cases, the same ardent pro-sucessonists Democrat politicians to regain political office, influence & power to reorganize bad habits, was a massive blunder.
Post war industry & education should have been pushed more then it was, naturally under new management. With the nation expanding westward, coupled with the age of inventions, Indian wars, railroad expansion, the major problem was the public was disinterested, coupled with tiring of tax funds heading south in order garrison troops in states which were enveloped in open rebellion during the Civil War.