I have submitted a paper in a journal 19 months ago and the manuscript is still under review. Up to present, I have contacted the editorial manager several times but the results have not changed. They always reply "your manuscript is still under review." What should I do in this case? Thank you for your comments.
Assuming you're in a field with a quicker response time (e.g., not mathematics), I would email the Editor-in-Chief directly (outside of the journal's system) an tell her or him that your article has been in review for 19 months and if you do not hear back from her or him within a set deadline (1 or 2 weeks) you pulling your manuscript from that journal.
I had a similar experience where a manuscript of mine sat in "under-review" for 12 months. The Editor-in-Chief apologized for the delay and promised me the review would be completed within a set deadline. In my case, the Editor-in-Chief was clearly unhappy with the Associate Editor I was assigned.
As long as you are polite, but firm, there is nothing wrong with being assertive.