BTW If Rhaegar and Lyanna were in love, why couldn't they just proclaim it openly. Robert and Ned started a bloody war because they thought that Rhaegar had kidnapped Lyanna. I know that Mad King had killed Ned's father and brother (reminds me of Daeny killiing Randyll and Dickon Tarly), but If Rhaegar and Lyanna had been more open about their relationship, then the whole war would not have started.
Enough to start a war over ? I don't think so.
Rhaegar was an idiot if you ask me. He annulled his marriage to Elia Martell so that he could get married to Lyanna. Fine but not telling the world about it led to Ned Stark's father and brother thinking that their sister had been kidnapped. That lead to the ill fated meeting with the Mad King.
This issue is that prince Rhaegar was already married, with two children. The picture has been unfolding slowly in the books and on the show, but the way it seems now, is that Rhaegar didn't love Ellia the same way she loved him.
Originally, Rhaegar was bethrothed to Cersei. This was Tywin's doing when he was Hand of the King to Aerys (the Mad King). Aerys and Tywin were feuding and scheming against one another. So, Aerys set up Rhaegar (the crown prince and next in line to be king) to be wed to the princess of Dorne (Ellia), instead of Cersei. Rhaegar fell in love with Lyanna Stark and the two of them ran away together (all Romeo and Juliet like) and were married in secret.
Presumably, he married Lyanna for love and married Ellia because he was commanded to. It should be noted that Rhaegar's children with Ellia (Jon's half-siblings) were between the ages of 1 and 3, when they were murdered by the Lannisters/when Jon was born. So Rhaegar nearly had 3 kids back to back to back. After having her second child with Rhaegar, Ellia nearly died giving birth and Aegon (Martell) was sickly at birth.
This was scandalous. Add in Lyanna being bethrothed to Robert and presumably just not that into him, as he was for her. Lyanna really was the "Helen of Troy" for Robert's Rebellion.
They could not proclaim it because Rhaegar was married. The Lords and Ladies of Westeros thought it was scandalous that when he won the Tourney of Harrenhal he choose Lyanna as the Queen of of Love and Beauty riding past his own wife to give flowers to Lyanna, their reaction to a relationship between a married prince and an highborn lady who was betrothed to another man would have met with even stronger disapproval.
Not just that, but would Rhaegar have even been allowed to get an anullment and be remarried so quickly? My knowledge of Medieval laws for martimony are lacking, but I was under the impression that a person could not get an anullment (different from a divorce) if a marriage had produced children.
@Littlefinger
This video is from 2014 and perfectly predicts all of Littlefinger's plans before the show revealed them.