March 1952: Ruhiyyih Khanum is appointed a Hand of the Cause

On 26 March, 1952, following the death of her father, Ruhiyyih Khanum was appointed, in his stead, a Hand of the Cause: "With sorrowful heart announce through national assemblies that Hand of Cause of Baha'u'llah, highly esteemed, dearly beloved Sutherland Maxwell, has been gathered into the glory of the Abha Kingdom. . . . The mantle of Hand of Cause now falls upon the shoulders of his distinguished daughter, 'Amatu'l-Baha Ruhiyyih-Kha num, who has already rendered and is still rendering manifold no less meritorious self-sacrificing services at World Center of Faith of Baha'u'llah." (Shoghi Effendi, message dated 26 March 1952; ‘Citadel of Faith’) 

March 1909: Baha’i Temple Unity is formed in Chicago, Illinois

In March 1909, a convention representative of various Bahá'í centers was called, in pursuance of instructions received from 'Abdu'l-Bahá. The thirty-nine delegates, representing thirty-six cities, who had assembled in Chicago, on the very day the remains of the Báb were laid to rest by 'Abdu'l-Bahá in the specially erected mausoleum on Mt. Carmel, established a permanent national organization, known as the Bahá'í Temple Unity, which was incorporated as a religious corporation, functioning under the laws of the State of Illinois, and invested with full authority to hold title to the property of the Temple and to provide ways and means for its construction. At this same convention a constitution was framed, the Executive Board of the Bahá'í Temple Unity was elected, and was authorized by the delegates to complete the purchase of the land recommended by the previous Convention. Contributions for this historic enterprise, from India, Persia, Turkey, Syria, Palestine, Russia, Egypt, Germany, France, England, Canada, Mexico, the Hawaiian Islands, and even Mauritius, and from no less than sixty American cities, amounted by 1910, two years previous to 'Abdu'l-Bahá's arrival in America, to no less than twenty thousand dollars, a remarkable testimony alike to the solidarity of the followers of Bahá'u'lláh in both the East and the West, and to the self-sacrificing efforts exerted by the American believers who, as the work progressed, assumed a preponderating share in providing the sum of over a million dollars required for the erection of the structure of the Temple and its external ornamentation. (Shoghi Effendi, God Passes By, p. 261)

March-April 1916: The first eight Tablets of the Divine Plan were revealed by ‘Abdu’l-Baha

The first eight Tablets were revealed between 26 March and 22 April 1916, and the final six between 2 February and 8 March 1917. Of the first group, five Tablets reached America and were published in the 8 September 1916 issue of Star of the West. After that, communication with the Holy Land was cut off and the rest of the Tablets remained in the vault under the Shrine of the Báb until the end of the war. They were dispatched to America and unveiled in a ceremony during the 'Convention of the Covenant' held at the Hotel McAlpin in New York in April 1919. (Wendi Momen, A Basic Baha’i Dictionary)