In sequence learning the objective is to capture short-term and long-term memory. The short-term memory is captured very well by standard RNN, however, they are not very effective in capturing long-term dependencies as the gradient vanishes (or explodes rarely) within an RNN chain over time.
The gradient vanishes when the weights have small values that on multiplication vanish over time, whereas in contrast, scenarios where weights have large values keep increasing over time and lead to divergence in the learning process. To deal with the issue Long Short Term Memory (LSTM) is proposed.