The Netherlands is the nation with the tallest people. Only 20 years ago they were below average I believe. Thanks to the improved diet of the average citizen great heights are now seen.
Average height has much more to do with nutrition than genes, the USA used to the tallest nation but now perhaps because other countries have shown a stronger initiative for providing nutrition to its people the tables have turned.
Genetically, it is known that the slavic people are the tallest. This is seen regions in Serbia where the average heigh of a man is over 6ft 2. The slavic people are known to be the tallest but the statistics do not reflect that because of malnutrition and low incomes preventing healthy living.
Hope this helped.