More than 1,000 buses, 37 trains, and 14 planes brought civil rights marchers from across the country to the 1963 March on Washington for Jobs and Freedom. (National Archives)

On Aug. 28, 1963, nearly 250,000 Americans descended on the nation's capital for the March on Washington for Jobs and Freedom. Organizers expected 100,000 marchers to attend, and more than double that number showed up, sending a message to the White House, Congress, and the world that their grievances needed to be addressed.

As we commemorate the 50th anniversary of this march where Martin Luther King Jr. delivered his "I Have a Dream" speech, we're reminded once again of the power of a peaceful protest, and the ability of Americans to come together to enact change.

And so, we want to know: What are the causes that you care most about today?

Let us know in the comments below - or share with us on Tw itter using the hashtag #IMarchFor .

And if you're on the National Mall on Wednesday look out for ABC News' "I March For…" posters. We'll be asking people to fill them out, so that we can share your responses during our television coverage and throughout the day on social media!