The United States of America has no law compelling any of its citizens to vote, in fact, there aren't any laws that compel a citizen to register to vote, yet there have been historically, very specific laws to preclude people, especially certain people, from being eligible to vote. The fact that in recent times in regards to Presidential elections that less than 60% of eligible voters bother to vote, doesn't tell the full story of how few people actually do vote, for there are millions of Americans that don't bother to even register to vote, or are precluded from voting via a felony conviction, or are effectively disenfranchised from voting, because they don't have the time, they have been intimidated, functionally illiterate, or their polling booth are not convenient, so to register and then to vote is too much trouble, or they are just ignorant of the whole matter.
At the inception of America, voting was only allowed for property owning males, specifically Protestant and white, which even at that time, was not a true reflection of all the citizens residing in America. Those whites that were born outside of America, first had to become naturalized, and if property owning, white, and Protestant, were thereby enfranchised to vote. Then, over a period of extended time, property qualifications were eased, religious restrictions less adhered to, and free black males in some States, were enfranchised. Despite the passage of the 15th Amendment in 1870, which essentially allowed all males, even those that had previously been enslaved to vote, those blacks so enfranchised, especially in the south, found that their ability to vote was soon nullified by the white ruling class of their respective State. In 1920, the 19th Amendment was ratified, allowing females to vote. In 1965, the Voting Rights Act passed allowing blacks and other minorities to bypass local laws that had effectively precluded them from being enfranchised and in 1971 the vote was extended to those that were 18 years old, whereas previously the voting age had been set at 21.
During all of this time, as those that were eligible to vote expanded, there was always the law that was on the books, as compared to the law in practice. So that, for blacks as well as other minorities, that were eligible to vote, found that when trying to register to vote, that they could not, because they were unable to pay poll taxes, or pass literacy tests designed specifically so that they would not be passed, or be physically intimated, or be threatened with loss of employment, or the registration was in the part of the community in which it was not safe to travel to, and so on and so forth.
Those that controlled the nucleus of the voting registration, made it their point to see that those that they wished to vote, voted, and those that they wished to not vote, did not. So that, even those registered to vote, could still be stopped at the polling booth, through intimidation tactics, outright violence, identification laws that were prejudicial against those that were poor, and so forth. In addition, besides the act of voting, there is the actual act and art of vote counting, of which innumerable elections have been accused of all sorts of fraudulent vote counts, of very suspicious natures, in order for the "correct" result to be certified and thereby approved.
The main reason so much has been done to get the "right" people to vote and have their votes counted, and for the "wrong" people to be disenfranchised and to have their votes nullified, is because voting actually matters. It matters as to who the elected officials are from the executive branch, to the legislative, to the judicial, to the equivalency of all these on a local and state level, to school boards, to propositions large and small, to taxation, and to everything else that is put up to the vote of the people, so that it most definitely matters who is permitted to vote, and how honestly those votes are counted, for the people are never truly represented unless each person is entitled and enfranchised for their own vote.