Here is one button:
<button type="submit" style="height: 30px; width: 120px">
<a href="https://www.world-affairs.org/get-involved/become-a-member/membership-2/individual-membership/" target="_blank">
Not sure it's kosher to put an anchor inside of a button. Especially when a button can act as an anchor. The problem I found was the target="_blank", but believe I got it.
Replace the above code with this
<button style="height: 30px; width: 120px;" onclick='window.open("https://www.world-affairs.org/get-involved/become-a-member/membership-2/individual-membership/");return false;'><h4>Individual</h4></button>
You have to do this for all buttons that you have an anchor inside of.