Case insensitive pandas dataframe.merge

Lowercase the values in the two columns that will be used to merge, and then merge on the lowercased columns

df_address['country_lower'] = df_address['Country'].str.lower()
df_CountryMapping['name_lower'] = df_CountryMapping['NAME'].str.lower()
df_merged = df_address.merge(df_CountryMapping, left_on="country_lower", right_on="name_lower", how="left")

df_merged = pd.merge(df_address, df_CountryMapping, left_on=df_address["Country"].str.lower(), right_on=df_CountryMapping["NAME"].str.lower(), how="left")