Geopandas: how to plot countries/cities?

I would need to plot some data on a geographic plot. Specifically, I would like to highlight countries and states where data comes from. My dataset is

    Year    Country State/City
0   2009    BGR     Sofia
1   2018    BHS     New Providence
2   2002    BLZ     NaN
3   2000    CAN     California
4   2002    CAN     Ontario
... ... ... ...
250 2001    USA     Ohio
251 1998    USA     New York
252 1995    USA     Virginia
253 2011    USA     NaN
254 2019    USA     New York

To create the geographic plot, I have been using geopandas as follows:

import geopandas as gpd

shapefile = 'path/ne_110m_admin_0_countries/ne_110m_admin_0_countries.shp'
gdf = gpd.read_file(shapefile)[['ADMIN', 'ADM0_A3', 'geometry']]
gdf.columns = ['country', 'country_code', 'geometry']

Then I have merged the two datasets:

merged = gdf.merge(df, left_on = 'country_code', right_on = 'Country')

and converted data to json:

import json

merged_json = json.loads(merged.to_json())
#Convert to String like object.
json_data = json.dumps(merged_json)

Finally, I have tried to create the chart as follows:

from bokeh.io import output_notebook, show, output_file
from bokeh.plotting import figure
from bokeh.models import GeoJSONDataSource, LinearColorMapper, ColorBar
from bokeh.palettes import brewer

geosource = GeoJSONDataSource(geojson = json_data)

#Define a sequential multi-hue color palette.
palette = brewer['YlGnBu'][8]
palette = palette[::-1]
color_mapper = LinearColorMapper(palette = palette, low = 0, high = 40)

tick_labels = {'0': '0%', '5': '5%', '10':'10%', '15':'15%', '20':'20%', '25':'25%', '30':'30%','35':'35%', '40': '>40%'}

color_bar = ColorBar(color_mapper=color_mapper, label_standoff=8,width = 500, height = 20,
border_line_color=None,location = (0,0), orientation = 'horizontal', major_label_overrides = tick_labels)

p = figure(title = 'Creation year across countries', plot_height = 600 , plot_width = 950, toolbar_location = None)
p.xgrid.grid_line_color = None
p.ygrid.grid_line_color = None

p.patches('xs','ys', source = geosource,fill_color = {'field' :'per_cent_year', 'transform' : color_mapper},
          line_color = 'black', line_width = 0.25, fill_alpha = 1)

p.add_layout(color_bar, 'below')

output_notebook()

#Display figure.
show(p)

When I run it, it says BokehJS 1.0.2 successfully loaded. but it does not display anything. My expected output would be one map where the colour is based on the number of appearance of a country (e.g. USA=5 would be the darker) and another one based on State/City (New York would be the darker).

Is there anything wrong in the code above?

(happy to share more data/info, if required)

from Geopandas: how to plot countries/cities?