def METHOD_NAME(df: pd.DataFrame) -> pd.DataFrame:
    """Country harmonization."""
    unharmonized_countries = df["country"]
    df = geo.METHOD_NAME(df=df, countries_file=str(N.country_mapping_path))
    missing_countries = set(unharmonized_countries[df.country.isnull()])
    if any(missing_countries):
        raise RuntimeError(
            "The following raw country names have not been harmonized. "
            f"Please: (a) edit {N.country_mapping_path} to include these country "
            f"names; or (b) add them to {N.excluded_countries_path}."
            f"Raw country names: {missing_countries}"
        )
    return df