Such insurers may invest in obligations of this State or those for which the faith and credit of this State are pledged for the payment of principal and interest, and in obligations of any other State in the United States, if within ten years immediately preceding the investment such State was not in default for more than ninety days in the payment of any part of principal or interest of any debt duly authorized by the Legislature of such State to be contracted by such State since the first day of January, 1878.