The protests sweeping the United States last weekend over the acquittal of George Zimmerman, a neighborhood watch coordinator who was charged with the second-degree murder and manslaughter of 17-year-old African-American Trayvon Martin, is a bitter reminder that racial tensions are still strong four and half years after the country elected its first African-American president.

In Oakland, California, protesters burned flags, vandalized police cars and smashed shop windows.

"And when you think about why, in the African-American community at least, there's a lot of pain around what happened here, I think it's important to recognize that the African-American community is looking at this issue through a set of experiences and a history that - that doesn't go away," President Barack Obama said, calling for calm.

"There are very few African-American men in this country who haven't had the experience of being followed when they were shopping in a department store. That includes me. And there are very few African-American men who haven't had the experience of walking across the street and hearing the locks click on the doors of cars. That happened to me, at least before I was a senator. There are very few African-Americans who haven't had the experience of getting on an elevator and a woman clutching her purse nervously and holding her breath until she had a chance to get off. That happens often," Obama added.

There is no doubt that the 2008 election of Obama as the first African-American president was a milestone toward racial equality.

There are other landmarks, too.

In the US capital, the Martin Luther King Jr Memorial is getting ready for the 50th anniversary of the famous March on Washington on Aug 28.

When I bought commemorative stamps in February that marked the 100th birthday of activist Rosa Parks, it occurred to me that the lives of African Americans are vastly different now.