There wasn't an understanding of it in those decades

Autism and Asperger were described already in the 1940s, the term Autism was already used in 1912.

The term Autism was popularised in 1943 by Leo Kanner in his paper: Kanner, L. (1943). Autistic disturbances of affective contact. Nervous Child, 2, 217-250.

He borrowed the term Autism from Eugen Bleuler, who used it to describe the introspection of adult schizophreniacs in Das autistische Denken. Leipzig und Wien (1912). Jahrbuch für psychoanalytische und psychopathologische Forschungen

Autism was already included in the ICD 9 which was finally adopted in 1975. The ICD-9-CM Diagnosis Code is 299.0 cf. http://www.icd9data.com/2015/Volume1/290-319/295-299/299/299.0.htm

The Journal of Autism and Childhood Schizophrenia (now Journal of Autism and Developmental Disorders) was founded as a peer-reviewed medical journal in 1971 and published by Springer.

Asperger was described by Hans Asperger in his Habilitation published as Die „Autistischen Psychopathen“ im Kindesalter in 1943, check out the PDF here.

Since his Habilitation was published in German and some other stuff happened around that time in Vienna, so it did not have a big impact.

Lorna Wing, a british psychiatrist, translated Asperger's work and published it in 1981 in Wing, L. (1981). "Asperger's syndrome: a clinical account". Psychol Med. 11 (1): 115–29. naming it Asperger's syndrome for the first time and popularising Asperger's work.

Uta Frith, a German developmental psychologist, focused on autism research since the early 1970s and later became a professor at the University College London. There she pioneered research in the Autism spectrum and the Theory of Mind. She also mentored Simon Baron-Cohen who currently leads a lot of research about autism spectrum syndromes and developed the empathizing–systemizing (E–S) theory.

I suggest to ask in a psychiatry subreddit to get detailed answers about how the treatment evolved.

• Aurnhammer-Frith, U. (1969). Emphasis and meaning in recall in normal and autistic children. Language and Speech, 12; 29-38.
• Frith, U. (1972). Cognitive mechanisms in autism: Experiments with color and tone sequence production. Journal of Autism and Childhood Schizophrenia, 2, 160-173.
• Frith, U., & Baron-Cohen, S. (1987). Perception in autistic children. In D. Cohen, A. Donnellan, & R. Paul (Eds.), Handbook of Autism and Disorders of Atypical Development. (pp. 85-102). New York: Wiley.
• Simon Baron-Cohen, Alan M. Leslie, Uta Frith, Does the autistic child have a “theory of mind” ?, Cognition, Volume 21, Issue 1, 1985, Pages 37-46,
• Baron‐Cohen, S. (2009), Autism: The Empathizing–Systemizing (E‐S) Theory. Annals of the New York Academy of Sciences, 1156: 68-80. doi:10.1111/j.1749-6632.2009.04467.x