Why did they feel it necessary to invade a country that has throughout history been so successful at repelling invasions? Did any of the Soviet high command take lessons from the United States' war in Vietnam about fighting guerrillas?
Here are past answers & discussions on the topic:
Key (hover over or click to view)
Reasoning Behind the Invasion
[7 c | 5 mo] Flaired Respondent | Immediate Events & Objectives
[7 c | 1 yr] Detailed Analysis | Afghan Politics & Initial Soviet Objectives
[13 c | 3 yr] Analysis | Internal Soviet & Afghan Issues
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#Related
Recommended Reading
[10 c | 3 yr] Annotated List | 10 Books
[6 c | 2 yr] Flaired Respondents | 5 Books
[4 c | 2 yr] Short Lists | 2 Books
Soviet Experience in Afghanistan
[97 c | 8 mo] Flaired Respondents | Comparing US in Vietnam to USSR in Afghanistan
[25 c | 2 yr] Summary & Counterfactual
[4 c | 1 yr] Detailed Analysis | Comparing USSR in WWII to USSR in Afghanistan