shapefile lines to merge

[CarlosCanas]

Hello, I have several shapefiles, each one representing a quadrant o a river basin. I want to make them "one only shapefile" representing the lines of this basin. I thought to use "union" in overlay tools, however it is only to join polygons, these shapes are lines. In total, I have 49 shapefiles with all tributaries (lines) of the basin.
any suggestions?

[847396730]

Load your shp into an mxd, then right click => Data => Export Data to export it as a feature class into a geodatabase of your choosing.  Then you can load the other shapefiles' data into that feature class by right-clicking the feature class => Load => Load Data...