def METHOD_NAME(state_df, states_to_include):
    """Returns a national level population dataframe that includes the given states.
       Meant to be called from other files to generate the data when we know the needed states.
       state_df: the state level population dataframe
       states_to_include: the list of state fips codes we want to include in the national total"""
    df = state_df.loc[state_df[std_col.STATE_FIPS_COL].isin(states_to_include)]
    df[std_col.POPULATION_COL] = df[std_col.POPULATION_COL].astype(int)
    groupby_cols = [std_col.RACE_CATEGORY_ID_COL, std_col.AGE_COL]
    df = df.groupby(groupby_cols).sum().reset_index()
    df[std_col.STATE_FIPS_COL] = constants.US_FIPS
    df[std_col.STATE_NAME_COL] = constants.US_NAME
    needed_cols = [std_col.STATE_FIPS_COL, std_col.STATE_NAME_COL,
                   std_col.POPULATION_COL, std_col.AGE_COL]
    needed_cols.extend(std_col.RACE_COLUMNS)
    std_col.add_race_columns_from_category_id(df)
    df[std_col.STATE_FIPS_COL] = df[std_col.STATE_FIPS_COL].astype(str)
    return df[needed_cols].sort_values([std_col.AGE_COL, std_col.RACE_CATEGORY_ID_COL]).reset_index(drop=True)