THE LABOR DAY HOLIDAY

Americans are celebrating the Labor Day holiday, a moment born as a salute to the nation's unionized workers that now has often morphed into a day of family gatherings marking the unofficial end of summer.

---------------This is my way to make it more understandable-----------------------

Americans are celebrating the Labor Day holiday, a moment

born as a salute to the nation's unionized workers

               (Ed group)

that now has often morphed into a day of family gatherings

                 (That clause)            

marking the unofficial end of summer.

               (Ing group)

----------------- 7 grammartical points----------------------- 

1.     Ed group giải thích chữ a moment. (apposition)

2.   A moment đồng nghĩa với the Labor Day holiday

3.   That clasue giải thích “the nation's unionized workers”

4.    Và marking giải thích “family gatherings”

  born as a salute to the nation's unionized workers =

5.     Which was  born as a salute to the nation's unionized workers

6.    
                  marking the unofficial end of summer =

7.     Which          marks    the unofficial end of summer.