Flexbox - 为什么链接不是排成一列，而是排成一行？

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html,
body {
  margin: 0;
  padding: 0;
}

nav {
  display: flex;
  background: #303f62;
  height: 150px;
}

ul {
  display: flex;
  padding: 0;
  height: 125px;
  flex-wrap: wrap;
  padding: 10px;
  flex-direction: row;
  justify-content: space-evenly;
  align-items: center;
}

.left {
  display: flex;
  flex-direction: row;
  justify-content: flex-start;
  align-items: flex-start;
  margin-top: 15px;
  margin-right: auto;
}

.right {
  margin-top: 15px;
  margin-left: auto;
  margin-right: 10%;
}

ul>a {
  margin-right: 5px;
  width: 150px;
  border: 1px solid transparent;
  text-align: center;
  color: #fff;
  background: #1e625b
}

ul>a:hover {
  background: #29857d;
  cursor: pointer;
}

aside {
  display: flex;
  justify-content: center;
  align-items: center;
  width: 20%;
  height: 600px;
  min-width: 220px;
  background: #303f62;
}

aside .links {
  flex-direction: column;
  justify-content: center;
  align-items: center;
}

.links>a {
  text-decoration: none;
  color: #fff;
}

.links>a:visited {
  text-decoration: none;
  color: #fff;
}


/*Media Queries*/

@media all and (max-width: 920px) {
  ul {
    flex-direction: column;
  }
  ul a {
    margin-right: 0;
    margin-bottom: 5px;
  }
}

<nav>
  <div class="left">
    <img src="logo1.jpg" alt="Лого">
  </div>
  <div class="right">
    <ul>
      <a>Главная</a>
      <a>О нас</a>
      <a>Контакты</a>
      <a>Сотрудники</a>
    </ul>
  </div>
</nav>
<div class="section">
  <aside>
    <div class="links">
      <a href="#">Статьи</a>
      <a href="#">Домой</a>
      <a href="#"></a>
      <a href="#"></a>
      <a href="#"></a>
    </div>
  </aside>
</div>