Please answer a question about the following article about Beyoncé:

In December, Beyoncé along with a variety of other celebrities teamed up and produced a video campaign for "Demand A Plan", a bipartisan effort by a group of 950 US mayors and others designed to influence the federal government into rethinking its gun control laws, following the Sandy Hook Elementary School shooting. Beyoncé became an ambassador for the 2012 World Humanitarian Day campaign donating her song "I Was Here" and its music video, shot in the UN, to the campaign. In 2013, it was announced that Beyoncé would work with Salma Hayek and Frida Giannini on a Gucci "Chime for Change" campaign that aims to spread female empowerment. The campaign, which aired on February 28, was set to her new music. A concert for the cause took place on June 1, 2013 in London and included other acts like Ellie Goulding, Florence and the Machine, and Rita Ora. In advance of the concert, she appeared in a campaign video released on 15 May 2013, where she, along with Cameron Diaz, John Legend and Kylie Minogue, described inspiration from their mothers, while a number of other artists celebrated personal inspiration from other women, leading to a call for submission of photos of women of viewers' inspiration from which a selection was shown at the concert. Beyoncé said about her mother Tina Knowles that her gift was "finding the best qualities in every human being." With help of the crowdfunding platform Catapult, visitors of the concert could choose between several projects promoting education of women and girls. Beyoncé is also taking part in "Miss a Meal", a food-donation campaign, and supporting Goodwill charity through online charity auctions at Charitybuzz that support job creation throughout Europe and the U.S.

The Demand a Plan video campaign followed what tragic event?
Sandy Hook Elementary School shooting.