I think that is a very jaundiced view. The "World War Adjusted Compensation Act" of 1924 had awarded them bonuses in the form of certificates they could not redeem until 1945. Each service certificate, issued to a qualified veteran soldier, bore a face value equal to the soldier's promised payment plus compound interest.
The law Congress passed stipulated that each veteran was to receive a dollar for each day of domestic service, up to a maximum of $500, and $1.25 for each day of overseas service, up to a maximum of $625 (2010: $7,899). Amounts of $50 or less were immediately paid. All other amounts were issued as Certificates of Service maturing in 20 years.[6]
Some 3,662,374 military service certificates were issued, with a face value of $3.638 billion (2010: $43.7 billion). Congress established a trust fund to receive 20 annual payments of $112 million that, with interest, would finance the 1945 disbursement of the $3.638 billion due the veterans. Meanwhile, veterans could borrow up to 22.5% of the certificate's face value from the fund; but in 1931, because of the Great Depression, Congress increased the maximum value of such loans to 50% of the certificate's face value.
On June 15, 1932, the House of Representatives passed the Wright Patman Bonus Bill which would have moved forward the date for World War I veterans to receive their cash bonus. The Senate voted the Wright Patman Bonus Bill down.
So they were not "extorting" money; the payments had been lawfully enacted by Congress and the accelerated payments act was passed by the House. Because of government mismanagement of the economy (particularly through the creation of the Fed) and disastrous economic decisions exacerbating the Great Depression, the vets were there to show support for passage of Wright Patman through Congress and plead their case.
That is hardly extortion.
“In 1781, most of the Continental Army was demobilized without pay. Two years later, hundreds of Pennsylvania war veterans marched on Philadelphia, then the capital, surrounded the State House where the U.S. Congress was in session, and demanded their pay.”
“The Pennsylvania Mutiny of 1783 (also known as the Philadelphia Mutiny) was an anti-government protest by nearly 400 soldiers of the Continental Army in June 1783. The mutiny, and the refusal of the Executive Council of Pennsylvania to stop it, ultimately resulted in Congress vacating Philadelphia and the creation of a federal district to serve as the national capital.”