I think you got bit by an issue Splunk has with using fields that include spaces in evals. A rename of the Destination Country Correct Translation to a field name with no spaces would have sorted it.
index = "myindex"
| rename "Destination Country Correct Translation" as Country
| eval Country = case(Country=="A","A",Country=="B","B",Country=="C","C",Country=="D","D",Country=="E","E",true(),"Others")
| stats sum("Declared Value _USD") as sales by Country
| eventstats sum(sales) as total_sales
| eval Percentage=sales/total_sales*100
| sort 0 - sales
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